Though group interventions are widely used in community-based and clinical settings, there are few brief instruments for assessing the group environment. Two studies on the development of a brief measure to assess intervention group environments are described, and psychometric properties of the new scale are presented. The new measure is based on Moos' (1994) Group Environment Scale (GES). Participants in the studies were from two independent randomized controlled clinical trials (RCTs) of group interventions (combined N=334). In Study 1 (N=139), the factor content of the original 90-item GES was examined. The scale was shortened, the response format was changed, and items were adapted and added to in an effort to increase applicability to community-based and clinical intervention groups. In Study 2 (N=195), the new scale was evaluated, the factor solution obtained in Study 1 was cross-validated, and subsequently the length of the scale was shortened again. The final scale contains 25 items with three subscales. Reliability and validity of the new scale was examined. Finally, the research and practice implications of the scale are discussed. (Contains 4 tables, 2 footnotes and 1 figure.)