Four hundred cases of transitional cell bladder cancer were reviewed by light microscopy for the presence of apoptotic cells in the primary tumour biopsy specimens. The number of apoptotic cells/mm2 of neoplastic epithelium (apoptotic index, AI) was related to various histological features and prognosis. AI was related significantly to high T-category, high grade, DNA aneuploidy, large nuclear morphometric variable values, and high proliferation rate of cancer cells. Tumours showing overexpression of p53 oncoprotein in over 10 per cent of the nuclei had significantly higher AI values than p53-negative tumours. Multivariate regression analysis showed that AI was independently predicted by mitotic index, mean nuclear area, and papillary status. Progression, recurrence-free survival, and survival of superficial tumours were all related significantly to AI. In multivariate survival analysis, T-category, papillary status, grade, and mitotic index had independent prognostic value, while the recurrence-free survival of Ta-T1 tumours was related independently to AI. The results show that AI is related particularly to mitotic activity in transitional cell bladder tumours, while AI as assessed by light microscopy hardly has any independent prognostic significance.