Objective: To assess the distribution of Body Mass Index (BMI) and the prevalence of obesity at the time of diagnosing diabetes in the primary care network in Kinshasa, democratic republic of Congo (DRC), from 1993 to 1999. Methodology: A total of 4967 patients with diabetes were classified according to BMI, age at diagnosis (<30 years versus <= 30 years), sex ans subsequent treatment (insulin treated versus non-insulin treated). WHO criteria were used to define diabetes and obesity. Results: One diabetic patient in 4 was underweight (26.4%). The prevalence of obesity was 8.1%. Undernutrition was more prevalent in male patients aged <30 years at diagnosis and, in contrast, obesity was more prevalent in patients aged <= 30 years at diagnosis, especially among women. Conclusion: Undernutrition is highly prevalent at the time of diagnosis in young diabetic patients in Kinshasa. The overall prevalence of obesity at diagnosis is relatively low, except in women diagnosed at >= 30 years of age. Prospective studies are needed in the Democratic Republic of Congo to characterize secular trends of undernutrition and obesity in order to improve preventive and management strategies.