We evaluated the immediate and long-term effects on immune function measures of a 6-week structure psychiatric group intervention for patients with malignant melanoma. Along with a reduction in levels of psychological distress and greater use of active coping methods, the following immune changes were seen at the 6-month assessment point in the intervention-group patients (n = 35) compared with controls (n = 26): significant increases in the percent of large granular lymphocytes (defined as CD57 with Leu-7) and natural killer (NK) cells (defined as CD16 with Leu-11 and CD56 with NKH1) along with indications of increase in NK cytotoxic activity; and a small decrease in the percent of CD4 (helper/inducer) T cells. At the 6-week follow-up point, the majority of these changes were not yet observable. The results indicate that a short-term psychiatric group intervention in patients with malignant melanoma with a good prognosis was associated with longer-term changes in affective state, coping, and the NK lymphoid cell system. Affective rather than coping measures showed some significant correlations with immune cell changes.