PROBLEM Poor knowledge and stigmatizing attitudes of healthcare professionals constitute a significant barrier to child and adolescent mental health care worldwide. This study aimed to determine the effect of a training intervention on the knowledge and attitudes of pediatric nurses to child mental health problems at a Nigerian tertiary hospital. METHODS A two group pretest-posttest study design was undertaken. A total of 156 pediatric nurses were recruited, and participants in the intervention group received a brief child mental health training based on the World Health Organization's mhGAP training manual. Knowledge and attitudes to child mental health problems were obtained at baseline, and post intervention. FINDINGS There were no differences in knowledge or attitudes across the two groups at baseline. Post intervention, there was a significant increase in the mean post knowledge scores of the intervention group compared with the control group (t = 3.8, p