The START predicts aggressive outcomes and to some extent self-harm. However, it is not known whether gender moderates its performance. This study used routinely collected data to investigate the predictive ability of the START for aggression and self-harm in secure psychiatric patients. Utility of the START was examined separately for men and women. The START was a stronger predictor of aggression and self-harm in women than men. The specific risk estimates produced large effect sizes for the prediction of aggression and self-harm in women; none of the AUC values reached the threshold for a large effect size in the male sample.