This investigation was undertaken to determine the relative importance of bladder neck prolapse and neuromuscular damage in the aetiology of stress incontinence of urine and to identify any tissue change in the pubocervical fascia associated with prolapse. Sixty women with stress incontinence and no previous surgery and twenty women with normal urinary control were studied. Bladderneck prolapse was assessed radiologically. Measurement of urethral closure pressure was made at rest and during stress. Neurophysiological assessment of the urethra and pelvic floor was made by single fibre electromyography and pudendal nerve terminal motor latency measurements. At operation biopsies of the pubocervical fascia were taken and studied histologically using Massons trichrome and acetylcholinesterase staining. Collagen was assessed using autofluorescence, hydroxy-proline assay and pyridinium link analysis. All stress incontinent women had reduced urethral closure pressures and neuromuscular damage to the pelvic floor. This damage was greatest in those stress incontinent women without prolapse. Histologically the same connective tissue elements were present in the pubocervical fascia of both groups of stress incontinent women, but there was greater smooth muscle denervation in those without prolapse. There was no difference in collagen content but there was a marked difference in the nature of collagen in women with stress incontinence and prolapse, compared to those women with stress incontinence alone.