The aim of our study was to assess the frequency and location of mitoses in routine haematoxylin- and eosin-stained sections of prostatic intraepithelial neoplasia (PIN) and then to compare the patterns with those in benign prostatic hyperplasia (BPH) and prostatic invasive adenocarcinoma (PAC). The frequency of mitoses in the epithelial cell layers increased from BPH through PIN up to PAC. The proportions of mitoses in PIN lesions of low grade (PINlow) and high grade (PINhigh) were greater than in BPH (mean 0.001%; standard error, SE, 0.001%), the values decreasing from the basal layer towards the lumenal. In PINlow, the mean category values were 0.087% (SE 0.04%) in the basal, 0.046% (SE 0.033%) in the intermediate and 0.024% (SE 0.024%) in the lumenal position. In PINhigh, the mean category values were 0.194% (SE 0.178%) in the basal position, 0.075% (SE 0.06%) in the intermediate and 0.049% (SE 0.033%) in the lumenal position. The proportions of mitoses in adenocarcinoma with cribriform pattern decreased from the basal towards the lumenal layer, as for PIN: 0.154% (SE 0.096%) in the basal position, 0.072% (SE 0.044%) in the intermediate and 0.064% (SE 0.04%) in the lumenal position. In the solid/trabecular adenocarcinomas, the mean category value in the cell layer adjacent to the stroma was 0.22% (SE 0.111%), whereas in the other cell layers it was 0.074% (SE 0.045%). In small and large acinar adenocarcinomas, the proportions of mitoses were 0.058% (SE 0.024%) and 0.068% (SE 0.019%), respectively. In conclusion, the evaluation of mitotic frequency and location in haematoxylin- and eosin-stained sections gives accurate information on how the mitotic activity in PIN compares with BPH and PAC.