Abstract: The aims of the study presented in this article were to validate the Swedish version of the Team Diagnostic Survey (TDS), and to examine effects of a feedback intervention to increase team effectiveness. The TDS is based on Hackman’s (2002) theory of group effectiveness which described three main criteria of performance and 14 factors that should affect team effectiveness. Participants in the survey were employees (N=533) across several different workplaces. Analyses were done at the group level, and data from 97 teams was included in the final data material. The sample (n=237) for the randomized field experiment consisted of 31 real life work teams from the larger survey sample (n=533/97). Results from validation data indicate that the TDS has satisfactory high Cronbach’s Alpha values on most factors. Cronbachs’s Alpha is a statistical measure of internal consistency; that is, how closely related a set of items are as a group. Results from the field experiment indicated that there was an overall increase in self-reported team effectiveness from first to second measurement. On several factors of team effectiveness a number were significantly higher for those receiving the TDS-based feedback. The outcomes suggest that group work practice might benefit from using research-oriented surveys such as the Team Diagnostic Survey as an effective feedback tool.