Patients with hereditary spastic paraplegia (HSP), a degenerative central nervous system disorder characterized by progressive lower extremity spasticity, frequently experience symptoms of voiding dysfunction. Urodynamic evaluation of patients with HSP has not been reported, and the etiology of voiding dysfunction remains unexplained. We present our evaluation of three men (ages 42-62 years) with this rare syndrome. Urgency of urination was a uniform and dominant complaint, and two patients regularly experienced urge incontinence. Other symptoms included frequency (n = 3), nocturia (n = 3), and diminished force of stream (n = 1). Postvoid residual volumes were less than 25 ml in all patients. On urodynamic evaluation the two patients with urge incontinence displayed cystometric evidence of involuntary detrusor contractions. Pelvic floor EMG recordings suggested detrusor-sphincter dyssynergia (DSD). In addition, one patient exhibited markedly diminished bladder compliance (1.0 ml/cm H2O) and capacity (50 ml). All patients reported marked symptomatic improvement when treated with continuous intrathecal baclofen. Evaluation during baclofen treatment revealed increases in bladder compliance and capacity, with apparent resolution of DSD in one patient. Voiding symptoms in these patients most likely arise from a neurogenic etiology; however, a contributory role for chronic outlet obstruction from striated muscle spasticity may also exist.