Neurophysiological measurements comprising surface electromyography (EMG) of the urethral and anal sphincters, measurement of the sensory thresholds of the dorsal nerve (DN) of the clitoris and the urethra and sacral reflex latencies from the dorsal nerve to urethra and anus and from the urethra to anus were performed in 44 females with genuine stress incontinence, in order to detect any relationship between the clinical disorder and a neurogenic defect in the innervation of the muscles involved in maintaining continence. Plain X-rays of the renal tracts (KUB films) were also studied to establish whether the prevalence of spina bifida occulta was increased in this group of patients and was a likely explanation for the nerve defects. Forty-three patients were found to have abnormal neurophysiological responses and the prevalence of spina bifida occulta was 50%, which compares with a prevalence of 17% in normal female controls. Genuine stress incontinence appears to be at least partly associated with defective innervation of the lower urinary tract and it is likely that in some cases the defect may be related to the presence of spina bifida occulta.