There has been much interest in the psychosocial issues faced by breast cancer patients because of the high prevalence of the disease and the severe psychological impact of the cancer itself, as well as its treatment. The objective of our study was to investigate the determinants of psychiatric morbidity among postoperative ambulatory breast cancer patients. The variables examined included the patients' biomedical characteristics, demographic characteristics, current concerns, coping responses and social support factors. Patients completed the Hospital Anxiety and Depression Scale (HADS) and the Mental Adjustment to Cancer scale (MAC scale), and information pertaining to demographic variables, current concerns and social support factors was obtained by a specially designed questionnaire. Available data were obtained from 148 randomly selected postoperative ambulatory breast cancer patients. The prevalence of psychiatric morbidity (including clinical anxiety and depression) evaluated by using the HADS cut-off point was 23%. The results of univariate analyses indicated that pain, dyspnea, having children with health problems, various other concerns (about children, other family members, the patients' own health and future treatment) and poor coping responses (low fighting spirit, high anxious preoccupation, high fatalism and high helplessness/hopelessness) were significant determinants of the patients' psychiatric morbidity. Additionally, in the logistic regression analysis, having children with health problems and having a low fighting spirit and a high helplessness/hopelessness were final significant determinants. Postoperative ambulatory breast cancer patients with these problems should be given careful attention, and psychosocial intervention may be beneficial for them.