Many women with breast cancer need psychological help to cope more effectively after treatment. Cognitive and behavioural techniques are not yet well established in France. A multi-site randomized study was conducted to evaluate the effects of a psycho-educational group intervention in this population. Two hundred and three patients, recruited after primary treatment, were randomly assigned either to a treatment group (psycho-educational intervention) or to a waiting-list control group. The 8-week programme of 2 h sessions comprised of thematic discussions, information and training in stress management techniques. Evaluation at baseline, after 8 sessions, and 1 month after programme completion, included evaluations using the STAI, POMS, MAC, EORTC QLQ-C30 and EORTC QLQ-BR23 breast module scales. We observed a significant reduction in anxiety (STAI, POMS) among group participants, a reduction in anger, depression and fatigue (POMS), a significant improvement in vigor and interpersonal relationships (POMS), in emotional and role functioning, in health status and fatigue level (EORTC QLQ-C30). In contrast, coping strategies (MAC) were not significantly different between groups. No group-related negative effects were observed and the global satisfaction levels were very high. This study demonstrates the feasibility and effectiveness of a psycho-educational intervention, which can accelerate the reduction of those negative affects which are present at the end of treatment. It represents an excellent complement or an alternative to individual psycho-oncologic therapeutic support, widely proposed in France, and should now be tested in groups with other types of cancer and at other disease phases.