The objective of this work was to classify and describe the different types of diabetic patients detected in West Africa. In four health centres (three in Ivory Coast, one in Niger) 310 new cases were detected and followed up over 1 year. Classification was based on age at diagnosis, BMI, ketonuria, basal and stimulated C-peptide levels at inclusion, and response to antidiabetic therapy. In this population, males were predominant (sex ratio = 2.40), and random blood glucose levels very high at screening (mean +/- SE, 18.6 +/- 0.4 mmol/l). Only one case of fibrocalculous pancreatic diabetes and one possible case of diabetes mellitus related to malnutrition were detected. IDDM was diagnosed in 11.3% of the patients, half of them above 35 years. Leanness was observed in 59% of the patients with NIDDM. A dramatic decrease of fasting blood glucose was observed in all groups after 2 months of treatment, especially in NIDDM. As IDDM and non-obese NIDDM presented great similarities before treatment, even for C-peptide levels, a point score system is proposed to classify these two groups at baseline. In conclusion, it is confirmed that the form of diabetes previously defined as related to malnutrition is a very rare entity in black African populations. In contrast, African diabetes is characterised by the high proportion of NIDDM patients with low BMI, and reduced beta-cell function, rarely associated to ketonuria. This form of diabetes seems to be adequately controlled with oral hypoglycaemic drugs and/or diet in the year following diagnosis.