The purpose of this study was to investigate the dispositional optimism-posttraumatic growth (PTG) relationship in postoperative breast cancer patients and to examine if perceived social support moderates this relationship. The study was conducted with 104 women undergoing postoperative chemotherapy treatment or coming to the hospital for their routine controls. Hierarchical multiple regression analyses indicated that breast cancer survivors high on dispositional optimism and perceived social support, are more likely to develop PTG. Among the different sources of social support, only social support perceived from a private person moderated the dispositional optimism-PTG relationship. Strengths, limitations and possible implications of the findings are discussed.