Antisocial behavior in childhood and adolescence is an unquestionably serious problem for society. Family-based treatments are promising but face the challenging obstacle of premature parental dropout. To systematically study dropout, we randomly assigned 147 families with a markedly aggressive child (age 4 to 9 years) to a standard family treatment (SFT) focusing exclusively on parental management or to an enhanced family treatment (EFT) that also promoted frequent discussions of adult issues. EFT produced a significantly lower dropout rate than SFT overall, but particularly for high-adversity families. Dropouts were clearly distinguishable from completers on several dimensions. The results underscore the importance of addressing contextual variables such as family adversity in the treatment of childhood antisocial behavior.