The effectiveness of inpatient group therapy was estimated in a meta-analysis of 24 controlled and 46 studies with pre-post-measures published between 1980 and 2004. Diagnosis, theoretical orientation and the role of the group in the particular treatment setting were used to examine differential effectiveness. Beneficial effects were found for inpatient group therapy in controlled studies (d = 0.31) as well as in the studies with pre-post-data (d = 0.59). Differences in the homogeneity of patient improvement effect sizes were found across different diagnostic categories. Furthermore, greater improvement was exhibited in mood disorder patients when compared to mixed, psychosomatic, post traumatic stress disorder (PTSD), and schizophrenic patients replicating recent findings from meta-analyses of outpatient group treatment. A comparison between controlled studies and pre-post-measure studies indicated no improvement for waitlist patients which contradicts previous reports. Implications for therapy and future research are discussed within the context of methodical considerations. PsycINFO Database Record