Acute urinary retention is an unpleasant, painful experience which requires immediate medical, and frequently surgical intervention. Population studies reveal that acute urinary retention is a common event: a 60 year-old man who survives a further 20 years has a 23 per cent probability of experiencing an acute episode of urinary retention. About half of acute retention episodes appear to be linked to general anaesthesia and a further large population due to the natural history of benign prostatic hyperplasia. The risk of acute urinary retention increases with increasing age. There are a number of other risk factors with risk increased in men with moderate and severe urinary symptoms, low peak urinary flow rates (less than 12 ml/sec) and among men with large prostates. Recent placebo-controlled randomised trials reveal that finasteride is associated with a 57 per cent reduction in the hazard ratio of acute urinary retention when used for at least two years. Since finasteride acts in a positive manner on the major risk factors (finasteride use increases peak urinary flow rate, reduces symptom scores in moderately symptomatic men and reduces prostate volume), this result is not too surprising. It remains to be determined what the risk factors for anaesthesia-induced acute retention are and how they can be altered. Nevertheless, the improvement of our knowledge of the epidemiology of acute urinary retention in the past 12 months is impressive.