Silver-stained nucleolar organizer regions (AgNORs) were studied in 90 patients with a single, primary, non-invasive papillary bladder tumour (stage pTa). All tumours were locally resected and patients were followed for 5 years (n = 68) or until the development of an invasive recurrence (n = 22). AgNOR counts showed wide overlaps between the different tumour grades. Furthermore, AgNOR counts were unable to predict the non-invasive recurrence pattern (none, single, multiple). Almost equivalent invasive recurrence rates were found among the following AgNOR counts and Bergkvist grades: AgNOR less than or equal to 5 (0%) and grade I (5%); AgNOR greater than 5, but less than or equal to 8 (20%); and AgNOR greater than 8 (77%) and grade III (67%). Combining the two parameters showed that an AgNOR count greater than 8 resulted in a 75 and 80% invasive recurrence rate in grade III and II tumours respectively. The reproducibility for AgNOR counting was moderate (kappa = 0.52) and no better than Bergkvist grading (kappa = 0.50).