Objective: The greater risk of abusing a step-child than a genetically related child has been attributed to discriminative parental solicitude. We tested whether it is better explained by antisociality, whereby more antisocial fathers are more likely both to have step-children and to be generally more violent. Method: We studied police reports of assaults on children by 387 domestically violent men who had a minor child, and their bivariate association with genetic relatedness, offender antisociality, and opportunity to assault step-children. In the subsample of 118 men with the opportunity to assault both step and genetically related children, we tested whether fathers were more likely to assault step-children, overall and among more antisocial men. Results: Number of step-children was associated with both child abuse and 2 of 3 measures of antisociality. When opportunity was controlled, fathers showed evidence of discriminative parental solicitude, being twice as likely to assault step-children as genetically related children. This step-father effect was observed at all levels of antisociality. Conclusion: Antisociality alone cannot explain the step-father effect. Discriminative parental solicitude remains a viable explanation for the step-father effect observed in this study. Research is needed to explore more proximal causes of the step-father effect. (PsycINFO Database Record (c) 2014 APA, all rights reserved)