Background: Comorbidity is common among child clinical samples. Reviews on effective intervention for
comorbid problems are lacking. Method: Based on a literature search of three databases (PsycINFO, MEDLINE
and ERIC), initial data analysis was carried out on 865 studies; of these,10 randomised trials fully met study
inclusion criteria and were subject to final analysis, with quality assessments and effect sizes calculated.
Results: Overall, effect sizes for externalising (M = 1.12) and internalising (M = 1.09) outcomes were
large. Effect sizes were large for family-based (M = 1.80) compared to individual (M = 0.78) and group-based
(M = 0.54) interventions. Studies with homotypic comorbidity (M= 1.18) displayed larger treatment effect
sizes than ones with heterotypic comorbidity (M = 0.54). Conclusions: While the overall quality ratings of the
reviewed studies varied from mediocre to good, with a variety of measures used across studies to assess the
same outcomes, findings suggest that current interventions are effective for reducing internalising and
externalising problems in children with comorbidity. More substantive evidence for the beneficial effects of
psychosocial interventions for children with comorbid problems may arise as more robust studies, which more
explicitly address and describe comorbidity, become available.