Migration has been associated with a higher risk of STI/HIV but few studies have assessed the sexual risk behaviour of migrant farm workers in Nigeria. An exploratory survey was conducted to assess the knowledge of HIV/AIDS and sexual risk behaviours of migrant farmers in Saki West Local Government Area, Oyo State, Nigeria. Questionnaires were used to obtain information on socio-demographic and occupational characteristics, knowledge of HIV/AIDS, sexual behaviours and history of STI symptoms. Overall 518 respondents were interviewed, slightly over half were aware of HIV/AIDS; awareness was significantly lower among the females, those aged 15-24 years and those with no formal education. Majority (80.7%) were sexually experienced, the mean age at sexual debut was 19.4 +/- 5.2 years and 18.4 +/- 4.2 years for males and females respectively. Sexual intercourse with multiple sexual partners in the past year was reported by 24.6% (males, 35.7%, versus females, 10.4%, p < 0.05). Recent sexual intercourse with a casual partner was reported by 9.1% (12.8% males versus 4.4% females). Only 18.2% used a condom during the last casual sexual contact. Level of awareness of HIV is unacceptably low and sexual risk behaviours are prevalent among these workers. Appropriate sexual health and HIV prevention interventions should be instituted.