Micturitional disturbance has attracted little attention in myotonic dystrophy, but detailed micturitional histories revealed that two out of six patients (33%) had micturitional symptoms. One had difficulty urinating and the other had urinary frequency, urgency and stress incontinence. Urodynamic studies were performed in all patients and the results were as follows: Two had low maximum urethral closure pressure, two had large and three had small bladder capacities, one had detrusor hyperreflexia and one had atonic cystometrogram. Urethral sphincter electromyography revealed a decreased bulbocavernosus reflex in one, and an absent anal reflex in two. Motor unit analysis of external sphincter was performed with one patient and showed polyphasic potentials. Dystrophic changes of the lower urinary tract muscles, as well as supranuclear type of pelvic nerve dysfunction, could cause micturitional disturbance in patients with myotonic dystrophy.