Thirteen centers participated in a multicenter database with systematic evaluation of US and Canadian patients who had adrenal medullary transplantation for Parkinson's disease. This voluntary registry collected demographic, safety, and efficacy data using the same scoring measures over a 2–year follow–up period. Baseline data on 61 patients and 2–year follow–up data on 56 patients were compared. Eighteen percent died during the study period, and one–half of these deaths were related or questionably related to the surgery. Of the remaining 45 patients with data, global improvement, defined as an improved summed score of the “on” and “off” motor and activities of daily living functions from the Unified Parkinson's Disease Rating Scale, occurred in 32% of the patients at 2 years after surgery. At follow–up, significant group improvement persisted in the amount of daily “on” time and the quality of “off” function, but other measures were no better than baseline. When the global improvement calculation was based on the total sample and included deaths and patients lost to follow–up as “not improved,” only 19% were improved 2 years after surgery. Twenty–two percent of survivors had persistent psychiatric morbidity not present prior to surgery. These data document a modest group improvement in “off” function after neurotransplantation, but a serious level of mortality and morbidity. © 1991 American Academy of Neurology.