Calculated effect sizes give optimism for the efficiency of structured group interventions with mentally disordered offenders. Each of the reviewed studies is open to bias. This is due to the difficulty for researchers in having access only to small patient populations and delivering the intervention themselves. This makes large studies and blinding of treatment conditions difficult. A central finding of this review of the evidence has been the similarities in the limitations of the studies included. In the past, little research had been carried out on the rehabilitation of offenders with mental disorders. This study presents the first systematic review of the efficiency of structured group interventions with mentally disordered offenders. The review described and evaluated 20 studies of structured group interventions with mentally disordered offenders in hospital environments with various degrees of security. The majority of the studies employed known treatment manual programs. A standardized search strategy, with complementary methods of data retrieval was employed to ensure a high degree of recall. Tables and references