Accuracy of risk assessment instruments in predicting violence may appear poor if substantial numbers of study participants subsequently reoffend non-violently instead of violently as predicted. This study examined effects of changing the violent outcome on predictive accuracy of five instruments (OGRS, RM2000(V), VRAG, PCL-R, HCR20) for 1,353 male and 304 female released prisoners in England and Wales. Adding self-reported violence to criminal convictions resulted in a moderate increase in violent outcome among women, but was small among men. After removing offenders who subsequently reoffended non-violently, significant improvement in accuracy was found on all instruments for men, but not women. We concluded that risk assessment instruments for violence may be more accurate than previously described, but improvement can only be achieved with certain samples. Instruments relying heavily on previous criminal history for predictive power can demonstrate improved accuracy, but only after removing non-violent offenders from samples with extensive previous offending.