The urodynamic findings of 29 patients with Parkinson disease (PD) and lower urinary tract symptoms were compared with those of nine patients with the Shy‐Drager syndrome (SD). All patients with PD had bladder contraction and normal filling pressures, and 90% had detrusor hyperreflexia. Among the patients with SD, 67% had detrusor areflexia, 33% had involuntary bladder contractions, and 45% had poor vesical compliance. In all patients with SD who had a voiding cystourethrogram, an open bladder neck at rest was demonstrated, but it was found only in those with PD who had prior prostatectomy. The electromyography of the external sphincter showed some form of lower motor neuron lesion in all patients with SD, but it was normal in 39% of PD patients and consistent with just involuntary sphincteric activity in 61%. A neurological evaluation of patients with typical and atypical Parkinsonism can assist in differentiating between these two entities.