Objective: Children with reading difficulties are at elevated risk for externalising (e.g., conduct disorder) and internalising (e.g., anxiety and depression) mental health problems. Reading ability is also negatively associated with self-esteem, a consistent predictor of child and adolescent mental health more broadly. This study examined whether self-esteem moderated and/or mediated relationships between reading ability and mental health. Method: One hundred and seventeen children (7–12 years) completed standardised reading assessments (Castles and Coltheart Test 2; CC2) and self-report measures of mental health (Strengths and Difficulties Questionnaire; SDQ) and self-esteem (Coopersmith Self-esteem Inventory). Non-verbal intelligence (IQ) was measured using the block design and matrix reasoning subscales of the Wechsler Abbreviated Scale of Intelligence, and was controlled for in all multivariate analyses. Results: Reading ability was negatively associated with internalising symptoms. This relationship was not moderated by self-esteem. Poor readers also reported more total difficulties and externalising symptoms, but only at low levels of self-esteem. There was no evidence that self-esteem mediated relationships between reading ability and mental health. Conclusions: Poor reading was associated with internalising symptoms. Self-esteem moderated the impact of reading ability on total difficulties and externalising symptoms, with high self-esteem buffering against negative impacts of poor reading. However, the reliability of the self-esteem scale used in the study was poor and findings need replication using a reliable and valid self-esteem measure, as well as other measures of child mental health. If replicated, future research should examine whether interventions aiming to improve self-esteem can reduce the risk of externalising problems in children with reading difficulties.