Obesity is increasingly a major health problem in parts of the developing world. It has reached epidemic proportions among Africans living in the Western Hemisphere; similar potential may exist in urban Africa. We explored this possibility in an urban setting in Nigeria, Africa's most populous nation. A screening survey was carried out among randomly selected 998 civil servants, 581 men and 417 women, in Ibadan, a major Nigerian city. Biographical data were collected using standardized questionnaires, and measurements of anthropometric indices, blood pressures and plasma glucose concentration. Obesity and overweight were defined by body mass index based on international criteria. Prevalence of obesity was 8.82% (confidence interval [CI] = 7.13%, 10.75%), overweight 17.45% (CI = 15.12%, 19.95%), and overweight plus obesity = 26.18% (CI = 23.47%, 29.03%). Prevalence of obesity among the women was 17.27% (CI = 13.76%, 21.24%) and for men 2.75% (CI = 1.58%, 4.43%). Among the women 42% were obese or overweight compared with 15% of the male population. Obesity and overweight were associated with higher socioeconomic status. Prevalence of obesity and overweight in the study population is comparable to rates seen in many industrialized countries, and rapidly emerging urbanized populations in Africa.