Background: Bowel dysfunction, including both slow transit constipation and defecatory dysfunction, is a frequent and often troubling nonmotor manifestation of Parkinson's disease (PD). A variety of agents are employed for the treatment of constipation in PD, but dissatisfaction with available treatment approaches is common. Relamorelin is a synthetic ghrelin agonist that has demonstrated prokinetic properties within the gastrointestinal tract. Methods: We carried out a multi-center, randomized, double-blind, placebo-controlled study of relamorelin in patients with PD experiencing chronic, inadequately controlled constipation. Results: Only 18 of an intended 56 subjects completed the trial, in part because of the unexpected occurrence of multiple partially complete bowel movements in constipated PD patients, which made many subjects ineligible for participation. Conclusions: Although recruitment goals were not met, which precluded demonstration of any potential beneficial effect of relamorelin, unique and important insights with regard to the nature of constipation in PD were recognized, which hopefully will lead to more effective clinical trials in the future. It is clear that what PD patients understand as constipation may be more complex than previously realized and does not appear to be characterized by decreased stool frequency alone. (C) 2017 Elsevier Ltd. All rights reserved.