HIV/AIDS is a rapidly growing epidemic in sub-Saharan Africa. Very few studies have focussed on outdoor workers. A cross sectional survey was conducted among automobile repair workers in Ibadan, Southwest Nigeria. A structured questionnaire was administered by interviewers to collect information on knowledge of transmission and prevention of HIV/AIDS and sexual practices among automobile repair workers. Twenty five questions were designed to determine knowledge about HIV/AIDS, each with a minimum score of 0 and a maximum of 1. Eight hundred workers participated in the study. They were all male aged between 12 and 80 years, mean 29.8 years. About half of the population were single. Majority (96%) had heard of HIV/AIDS. Over 95% of respondents knew about transmission by sexual intercourse and blood transfusion. A mean knowledge score of 17.6 out of 25 was recorded. Several misconceptions such as transmission of HIV/AIDS by mosquitoes and through sharing of clothes were prevalent. Ninety-three percent had ever had sexual intercourse and 87% of singles were sexually active. Two hundred and thirty-nine, (30%) had casual sex partners. Of these, only 59% used condoms during the last sexual intercourse with casual partners. In spite of a high knowledge score among this male dominated low income workers, their sexual practices are such that will encourage transmission of HIV.