The importance of gender and obstetric factors as predictors of the age of onset of schizophrenia is debatable. Unfortunately, there is a significant dearth of studies in developing countries such as Nigeria. This study involved a survey of patients with schizophrenia (n = 1,445; N = 2,393), from March 2014 to March 2016, from a psychiatric hospital in southwest Nigeria. Structured diagnostic interviews were used to confirm diagnosis. Females had a higher age of onset (M = 34.91, SD = 15.52) compared with males (M = 28.78, SD = 10.62; p = .00, M = 32.74 ± 12.96). Gender and marital status were the only variables significantly related to the age of onset (p = .00). Our model predicted 10.1% of the variability in the determination of the age of onset of schizophrenia. (PsycINFO Database Record (c) 2019 APA, all rights reserved).