Aim: Overall aims were to evaluate a stress management intervention with a stepped care approach among women with breast cancer and to explore distress, emotional reactivity and fatigue, both using a theoretical approach and self-reported assessment. Methods: A total of 821 women were approached, 372 women rejected participation, 23 women failed to return the questionnaire and one died, hence, 425 patients (52%) accepted participation. Study I evaluated the cognitive processing model with the aid of an untreated patient group, including 189 women according to the main study protocol. Sixty-six of these women were ineligible for the intervention, as they did not report clinical levels of distress. The remaining 123 women were eligible but they declined participation. Study II explored the validation of the ELSS and emotional reactivity among women with breast cancer. The population comprised of all 425 women (breast cancer sample) and 176 women randomly selected from the PAR register (random women sample). Studies III and IV evaluated the intervention and included all 425 women. Main findings: Study I: avoidance does not mediate the relationship between intrusion and later psychological distress in an early stage breast cancer population. Study II: the ELSS has acceptable validity and reliability. The factor structure of the ELSS was similar in both samples and correlated well with the STAQ (gold standard). Younger age was the only variable associated with emotional reactivity at the start of curative treatment. Studies III and IV: a stepped care approach did not reduce the number of women who require a more extensive treatment at three-months post-diagnosis. Both intervention groups (group/individual) reduced their levels of distress, but there were no significant differences between them. Only about half of the women who were randomised in the second step of the intervention accepted participation. Conclusions: The present thesis provides information regarding distress, emotional reactivity and fatigue among women with breast cancer. A majority of women with early stage breast cancer seem to process the trauma of a cancer diagnosis in a satisfactory way but may experience some emotional reactivity, and younger women may experience more emotional distress. The results also highlight the need for validated measures and carefully planned psychosocial interventions.