Summary: In clinical practice, child psychologists' case formulations are often based on parental reports. In this study, we examined whether mothers' reports of internalizing and externalizing behavior problems in their children might be biased by maternal psychopathology. The target child sample consisted of 68 boys aged 6-12 years who were receiving treatment. Mothers' reports were compared with the reports of both teachers and group care workers as criterion ratings. After controlling for variance shared with the independent raters, multiple regression analysis indicated substantial partial correlations between various types of maternal psychopathology and the reporting of internalizing child behavior problems. Only small to insignificant partial correlations were found in the case of externalizing behavior problems. This finding is consistent with the social attribution theory that predicts greater distortion when observing more ambiguous stimuli.