The expression of c-myc proteins was analysed immunohistochemically in a series of 206 breast carcinomas with special focus on established prognostic factors and patient survival. Nuclear expression of c-myc proteins was detected in 12% of carcinomas, and it was related to the lack of estrogen receptors (p= 0.05). Cytoplasmic expression of c-myc was present in 95% of the tumours. Expression of cytoplasmic c-myc at the invasive margin was related to tumour grade (p= 0.0013), low mitotic index (p= 0.0002) and low S phase fraction (p= 0.026), and weakly associated with distant metastasis at diagnosis (p= 0.06) and to a high proportion of intraductal growth (p= 0.08). Long recurrence-free survival of the patients was related to strong cytoplasmic expression of c-myc at the invasive margin in the entire series (p= 0.0049) and in axillary lymph node-negative (ANN)(p= 0.0028) tumours. Cytoplasmic c-myc expression in the central areas of the tumour predicted metastasis at diagnosis (p= 0.002), non-ductal type of growth (p= 0.018) and low mitotic index (p= 0.005). Expression of c-myc in the stroma was related to the lack of estrogen receptors (p= 0.02) and to high S phase fraction (p= 0.01). The results show that overexpression of c-myc is involved in a highly complex manner with the early stages of breast cancer development, but it shows hardly any independent prognostic value over standard prognostic factors in clinical disease.