Uninhibited urethral relaxation appears to be a clinically distinct cause of urinary incontinence. It was found in 11 of 534 incontinent women who had multichannel urodynamic evaluation, and in 2 of these it was the sole cause of incontinence. This diagnosis should only be made after careful scrutiny has ruled out a low pressure detrusor contraction, cough, valsalva, or heel bounce as the cause of the urethral relaxation. Because the majority of patients had a voiding mechanism that included a detrusor contraction, it is unlikely that uninhibited urethral relaxation represents a variant of detrusor instability in patients unable to generate a detrusor contraction. It most likely reflects an exaggeration of urethral instability due to relaxation of the smooth and/or striated urethral musculature.