Analysis of cancer registration survival data, together with a review of published clinical and pathological studies, strongly suggests that cancer of the prostate occurring before the age of 55 has a worse survival prospect than at ages up to 74. The likely reasons appear to be a higher degree of malignancy of tumours in younger men and, particularly, late diagnosis from failure to suspect the disease in this age group. This suggests that routine clinical examination of the prostate should be carried out as soon as feasible after the age of 40.