In 17 patients, 15 women and 2 men, acute retention of urine developed in association with an attack of anogenital herpes. Constipation, blunting of sensation over the 2nd and 3rd sacral dermatomes, and neuralgic pains in the same area (with absence of the bulbocavernosus reflex in some individuals) suggested localised lumbosacral meningomyelitis with involvement of mainly sacral-nerve roots. The urinary dysfunction persisted on average for ten days and in 4 patients was severe enough to warrant catheterisation. Anogenital herpes should always be considered as a possible cause of acute retention of urine in sexually active young people and the possibility of occult herpetic infection of the cervix and rectum should be investigated.