The prognostic significance of silver-stained nucleolar organizer regions (AgNORs) was retrospectively studied among 230 patients with operable invasive breast cancer from a defined urban population. The number of AgNORs was evaluated from routinely processed paraffin sections by light microscopy at a total magnification of x630. The number of AgNORs had no predictive value on the 8-year survival rate corrected for intercurrent deaths (P = 0.2). A high number of AgNORs (> 2.7, the median value) was not related to any other prognostic variable studied except a low S-phase fraction measured by flow cytometry. AgNOR counting does not appear to be a useful prognostic variable in breast cancer.