Type 2 diabetes (T2D) is a major public health problem. The main concern of T2D is the increasing prevalence, life threatening complications, and huge costs of the management of T2D. Several factors, such as age, sex, socioeconomic status, area of living and obesity may affect the achievement of treatment targets for T2D patients. In addition, co-morbidities are very common in T2D patients which further complicates the treatment and increases the cost of management of T2D. Cardiovascular diseases (CVDs) and mental disorders are common co-morbidities associated with T2D. CVD is a major contributor of T2D mortality and mental disorders affect the self-management of T2D patients. T2D patients with comorbid diseases are often reported having worse quality of diabetes care, more complications and poor achievement of treatment targets. The aim of this study is to explore the treatment outcomes for different patient groups of the T2D cohort of North Karelia, Finland from 2011–12 to 2015–16, encompassing all T2D patients in the 13 municipalities of the region. Specifically, the study assesses the disparities between the process of care and treatment outcomes among T2D patients with and without CVD or mental disorders, also considering the age and sex. This study is designed as a register-based retrospective cohort study using the data from the regional electronic health records (EHR) of North Karelia, Finland from the period of 2011 to 2016. All the patients who had visited the public healthcare with a diagnosis of T2D (ICD-10 code E11) were identified from the regional EHRs. The study included 10,190 T2D patients who were alive at the end of 2012 and aged more than 20 at baseline (2011–12). At the end of 2016 there were 8,429 T2D patients alive and available for the follow up. Data on patients’ age, sex, HbA1c and LDL levels, permanent diagnoses and e-prescriptions were used in the study. Two process indicators and two intermediate outcome of care indicators were used to assess the quality of T2D care. HbA1c and LDL monitoring and management rates were analysed. Glucose lowering medications were categorised into five groups and lipid medications were categorized into four groups. The effect of intensification and de-intensification of different treatment lines on achievement of treatment targets by different patient groups was also analysed in this study. Basic characteristics of patients were described with counts, percentages, and mean values. Achievement of treatment targets by different patient groups and use of medications were expressed with percentages. Logistic and linear regression models with generalised estimating equations (GEE) were used. Along with unadjusted results, age and sex adjusted results were presented. P-values of less than 0.05 were interpreted as statistically significant. Transition plots were used to illustrate the fluctuation of achievement of treatment target and trend of use of glucose lowering medications by different patient groups during the follow-up. For the whole T2D cohort of North Karelia, the monitoring of HbA1c levels improved but a gradual deterioration was observed in the achievement of target HbA1c levels. In contrast to that, LDL monitoring and the achievement of target LDL levels improved during the follow-up. This study did not find any sex difference in the monitoring of HbA1c and LDL levels during the follow-up. However, there was some difference in the achievement of LDL targets and males showed better LDL control compared with females. Comparing the quality of diabetes care for T2D patients with and without mental disorders, improvement in the monitoring of HbA1c and LDL levels among all T2D patient groups, except those with dementia was found. The achievement of HbA1c targets declined while the achievement of LDL targets improved for all patient groups irrespective of having mental disorders. Comparing different medication groups with the achievement of treatment targets for T2D patients with and without co-morbidities showed that metformin was the primary choice of treatment for all patient groups. However, the use of metformin alone declined during the follow-up and the use of metformin and/or other non-insulin medications increased. T2D patients who had both mental disorders and CVD were mostly treated with a combination of insulin and non-insulin medication. A rise in the use of insulin alone was also observed among this group during the follow-up. A deterioration in the achievement of HbA1c treatment targets was observed during the follow-up despite the intensification of medication among all patient groups. However, the achievement of LDL treatment targets improved during the follow-up. In present study, many patients with T2D+Any mental disorder (AMD) and T2D+CVD+AMD were not using any lipid lowering medication, both at the baseline and follow-up. In nutshell, the monitoring of HbA1c and LDL levels improved during the follow-up for the T2D cohort of North Karelia, Finland irrespective of sex and co-morbidities. Patients had equal access to follow-ups. However, the achievement of glycaemic treatment targets declined for all T2D patients regardless of having CVD, mental disorders, or intensified treatments. It seems that maintaining the recommended glycaemic target in the long run is difficult for T2D patients as several factors affect the achievement of the treatment targets. Improvement in the achievement of LDL targets was observed in general for all T2D patients during the follow-up. However, sex disparities in the achievement of LDL treatment targets are a matter of concern. Females had higher LDL levels compared with males, which needs more attention. The large number of T2D patients with CVD and AMD not using any lipid lowering medication is also a concerning issue, increasing the risk of CVD events for this group. Active monitoring of patients, tailored treatment and intense patient education regarding T2D management needs attention to improve the quality of T2D care.