Several studies have been carried out on the prevalence of overweight and obesity among adults in urban areas of Nigeria, however there is insufficient data for the prevalence among the rural dwellers. It is also not clear if there is any difference in the prevalence of overweight and obesity between the rural and semi urban areas of Nigeria. A cross sectional study of anthropometrical parameters (weight and height) and body mass index (BMI) was conducted among 600 selected adult males and females in Iwo (a semi urban) local government area and Aiyedire (a rural) local government area of Osun State, South-Western Nigeria between August and October 2006. Pretested interviewer- administered questionnaires were used to obtain information on the socio-economic profiles, food consumption pattern and nutritional knowledge of the subjects. The prevalence of underweight, overweight and obesity in Iwo local government area were 4.7%, 25.3% and 11.3% respectively with 58.7% of the subjects falling within normal weight range. In Ayedire local government area, the prevalence of underweight, overweight and obesity were 7.3%, 22.3% and 13.6% respectively while the remaining 56.8% of the subjects studied fell within normal weight range. There was no significant difference (P value 0.38591) in the prevalence of overweight and obesity between the two local government areas.