Introduction: The true burden of child sexual abuse in Nigeria is not known as most reports are institutional based. This study was designed to determine population level data on the burden and pattern of child sexual abuse among adolescents in South Western Nigeria. Methods: A community based study among adolescents in SouthWestern Nigeria. Semi- structured interviewer administered questionnaire was used to collect data from respondents selected through a multistage sampling technique. Analysis was with SPSS version 20. Results: 398 adolescents (314 females and 84 males) aged 10-19 years with a mean age of 15.6 ± 2.0 years participated in the study. Most were single (90.7%), in school (84.2%), and lived with their parents/guardians (89.4%). The prevalence of CSA was 25.7%. Penetrative abuse occurred in 7.5%, and forced abuse in 46.2% of cases. Perpetrators were mostly boyfriends (31.2%) and neighbours (16.1%). Intra-familial abuse occurred in 7.5% of cases. Only 34.4% of cases ever disclosed the abuse. Conclusion: CSA is common in the community, with perpetrators majorly persons known to the adolescents. A large number of cases are not reported. Efforts should be made to educate children and their parents on various ways to reduce child sexual abuse and its consequences.