During one year 151 patients with 154 strokes were studied prospectively to determine the occurrence and outcome of urinary incontinence after a stroke. Seventeen per cent had pre-existing urinary incontinence. At 1, 4 and 12 weeks, 60%, 42% and 29% of the survivors, respectively, were not continent. Cystometry was performed in those with moderate or severe urinary incontinence persisting 4 weeks after the stroke. Detrusor instability was present in 85% of those who had been continent prior to their stroke. Factors associated with urinary incontinence at 4 weeks were moderate or severe motor deficit, impaired mobility and mental impairment (P less than 0.001). Two-thirds of patients with mild urinary incontinence at 4 weeks regained continence by 12 weeks.