SUMMARY Nigeria has one of the largest burdens of orphans and vulnerable children (OVC) in the world and psychiatric morbidity among OVC is a major global health problem. There are several previous studies on psychiatric morbidity among OVC in the world, however in Nigeria; there is a dearth of published research on the prevalence and factors associated with psychiatric morbidity among OVC. Objective: To determine the prevalence and factors associated with psychiatric morbidity among a sample of orphans and vulnerable children in Osun state, Nigeria. Method: A total of three hundred and fifty OVC were recruited from a non-governmental organization, Destiny Development Initiative (DDI) for the study. These OVC were selected from 3 sample areas, Ilesa, Ede and Osogbo. A cross sectional design was adopted and multi stage sampling technique was used. OVC were selected from the three areas using probability proportionate to size sampling method and respondents were selected using the simple random sampling (balloting method). Each child first completed the OVC Vulnerability Index (OVI) form to ascertain their vulnerability state. Then they were administered the socio-demographic questionnaires, Rosenberg Self-Esteem Scale (RSES) and Duke UNC Functional Social Support Questionnaire, (FSSQ). Respondents were screened for risk of psychiatric morbidity using the Strength and Difficulty Questionnaires (SDQ), while MINI-Kid (Mini International Neuropsychiatric Interview) Questionnaire was used to make psychiatric diagnosis. The Statistical Package for Social Sciences (SPSS) software version 21 was used for data analysis. Results: The mean age of the respondents was 14.7 years (± SD=1.36). There were more female respondents (n=181, 51.7%). Almost half of the parents of the respondents (48.2%) were married while a third (33.1%) were widowed. Of the 350 respondents, 46.3% were orphans of which the majority (70.4%) were paternal orphans, 22.8% were maternal orphans and 6.8% were double ii orphans. Most of the respondents (70.3%) were classified as vulnerable” while 29.4% were “more vulnerable”. Almost two-third of the respondents (62.6%) had experienced discrimination, about one-third (32.6%) experienced neglect, almost one-quarter (23.7%) experienced physical abuse, one–fifth (19.1%) emotional abuse, 12.0% had witnessed domestic violence and 1.4% had been sexually abused. Most of the respondents (94.9%) were from poor background and more than half (55.1%) were involved in child labour. All respondents (100%) attend school, but majority (68.3%) of the respondents had been absent from school in the past year for both financial (54.4%) and medical (45.6%) reasons. Almost a quarter (22.2%) miss school weekly, most (95.4%) of the respondents felt sad following school absenteeism and above half (55.1%) of the respondents reported good school performance. One out of every seven (15%) respondent had low self-esteem, and about half of the respondents (50.9%) reported low social support. The weighted prevalence of psychiatric morbidity among OVC was 38.0%. Depressive disorder had the highest prevalence (14.0%) while psychotic disorder had the lowest weighted prevalence (0.9%). There was no statistically significant association between psychiatric morbidity and orphan status of respondents (χ2 = 0.005, p = 0.945). However, there was statistical significant association between presence of psychiatric disorder and alcohol use (χ2 = 4.995, p = 0.034), emotional abuse (χ2 = 9.08, p = 0.003), experience of neglect (χ2 = 5.03, p = 0.025), living with disabled parents/guardian (χ2 = 6.35, p = 0.033) and school absenteeism (χ2 = 7.09, p = 0.008). Multiple logistic regression analysis showed that use of alcohol (OR=4.9), emotional abuse (OR=1.9) and school absenteeism (OR=1.8) were significantly associated with psychiatric morbidity among OVC. Conclusion: This study revealed high prevalence of psychiatric morbidity among OVC. It has also shown that psychiatric morbidity was association with the use of alcohol, child abuse (emotional abuse/neglect), physically disabled parents/guardian and school absenteeism. Thus, psychiatric iii morbidity and associated factors should be targets of preventive mental health interventions among OVC. 4