The expression of insulin-like growth factor II (IGF-II) was analysed immunohistochemically in a series of 211 breast cancers with special reference to standard prognostic factors and patient survival. IGF-II was expressed both in the cancer cells and in stromal cells, in 84% and 50% of cases, respectively. IGF-II expression in cancer cells was related to a non-metastatic disease at diagnosis (p = 0.03), low tumour grade (p = 0.02), DNA diploidy (p = 0.02) and S-phase fraction under 7% (p = 0.001). IGF-II negativity was positively correlated to morphometric SD of nuclear area (p = 0.0003), nuclear perimetry (p = 0.002), SD of nuclear perimetry (p = 0.02), minimum nuclear diameter (p = 0.005) and maximum nuclear diameter (p = 0.003). The expression of IGF-II in stromal cells was related to low histological grade (p = 0.02), mitotic index under 10/mm2 (p = 0.01), mild nuclear pleomorphism (p = 0.03), DNA diploidy (p = 0.08), SD of nuclear area (p = 0.006), mean nuclear perimeter (p = 0.05), minimum nuclear diameter (p = 0.005) and maximum nuclear diameter (p = 0.007) in that the nuclear factor values were higher in tumours without stromal IGF-II expression. In univariate and multivariate survival analysis, immunohisto-chemically detected expression of IGF-II had no independent prognostic value over standard prognostic factors. Despite the fact that expression of IGF-II was inversely related to several histopathological features of malignancy, the clinical behaviour of breast cancer seemed to be independent of IGF-II expression.