Aims The aim of this study is to determine the impact of the COVID-19 pandemic on the management and disease control of the patients with diabetes mellitus in Kocaeli. Methods This study was carried out in six leading central hospitals in five major districts of Kocaeli. The study was conducted between June 2020 and November 2020. The patients who had previous admissions to these clinics within 6 months prior to the pandemic were enrolled in the study. Results A total of 283 patients were enrolled in the study, among them 151 (53%) patients were female, 268 (95%) had type 2 DM and remaining 5% had type 1 DM. The median weight of the patients was similar between the previous and last visits (84 kg vs 83 kg, p = 0,88). Laboratory parameters of previous and current visits revealed that mean fasting plasma glucose (FPG) and HbA1c levels were not significantly changed. The number of the patients who had controlled blood pressure was significantly decreased. The number of those who had neuropathic complains and the severity of dyslipidemia significantly increased during pandemic period. Conclusion Our study demonstrated that despite decreased compliance with diet and exercise, and difficulty in accessing medication, there was no significant change in weight, FPG and HbA1c levels in diabetic patients. Since cultural differences, education level and socioeconomic opportunities differ between societies, national and international studies will be more accurate to evaluate the effects of epidemics on the course of chronic diseases.