The long‐term effect of selegiline (L‐deprenyl) in the treatment of Parkinson's disease has not been clearly delineated. We report on a group of patients whose treatment was initiated with selegiline (n = 43) and then subsequently included L‐dopa‐carbidopa (Sinemet) and in whom an extended period of observation was carried out; they are compared to a group of patients whose treatment consisted of L‐dopa‐carbidopa alone (n ' 39). In each, serial observations of the parkinsonian state and the response to treatment on a yearly basis for a period of 5 years were performed. No significant difference in the Hoehn‐Yahr stage or in the motor subscores of tremor, rigidity, bradykinesia, and gait‐posture was found between the two groups, nor was there a significant difference in the incidence of fluctuating responses or dyskinesias. The group that received combination therapy required less L‐dopa than did the group that received L‐dopa‐carbidopa alone during the first 3 years of treatment and a similar trend was evident in years 4 to 5. We conclude that minimal benefits accrued to the parkinsonian patients from long‐term use of selegiline. No clinical evidence to support the claim of “neuroprotective” properties was found. Selegiline's major usefulness is to modify the fluctuating therapeutic response seen with L‐dopa‐carbiodopa.