Purpose. In Western Australia approximately 450 violent offenders per year are referred to a cognitive-behavioural anger management programme (Skills Training for Aggression Control; STAC). Efficacy of the STAC programme with male adult inmates was investigated in two studies. Methods. A pre-test-post-test non-equivalent group design was utilized for Study 1 (N = 39) and Study 2 (N = 50). Violent offenders participating in STAC programmes were compared to a waiting-list control group on the dependent variables of anger knowledge, trait anger, anger expression, observed aggressive behaviour, and prison misconduct. Differential treatment effects according to trait anger level were examined in Study 2 anticipating greater gains for high trait anger violent offenders. Results. Data analyses provided little support fur the hypothesized STAC participants' treatment gains relative to the control group participants. Hypothesized differential treatment effect by trait anger level was not supported. Conclusions. Based on the limited support for the STAC programmes' treatment efficacy, caution is recommended before implementing anger management programmes with violent offenders.