This retrospective observational study investigated the prevalence of obesity in persons with type 2 diabetes, trends in obesity resulting from the duration and treatment of diabetes, and treatment-related changes in HbA1c and body mass index (BMI). Data on 1773 type 2 diabetics (802 men and 971 women) were obtained from the CroDiabNET registry. Follow-up included the analysis of patients' age, disease duration, diabetes treatment, BMI and HbA1c values. A significantly higher rate of overweight and obesity was found in persons with type 2 diabetes as compared to the general population. A significant decrease in BMI was observed in the groups treated by diet, and in those treated by oral hypoglycaemic agents (p < 0.05), regardless of their pharmacotherapeutic group, in contrast to a significant increase in BMI observed in the groups treated with insulin (alone or in combination with oral hypoglycaemic agents) (p < 0.05). Persons with type 2 diabetes lost weight only during the first years of the disease, while with diabetes duration and insulin treatment they regained weight. A significant increase in HbA1c was observed in the groups treated with sulfonylureas (p < 0.05), whereas all other groups revealed either a significant decrease (p < 0.05) or no change in HbA1c. Our findings suggest the necessity of an integrated approach to managing type 2 diabetic patients that would simultaneously address both diabetes and obesity. Good glycaemic control is imperative and diabetes treatment should not be postponed. Because of a possible concomitant weight gain, aggressive weight control measures should be applied concurrently in order to achieve maximum treatment benefit.