Constipation is one of the main and disabling nonmotor symptoms in Parkinson's disease (PD), with a prevalence ranging from 24.6% to 63% according to the different diagnostic criteria used to define chronic constipation. Constipation is currently recognized as a risk factor of PD in relation to the number of evacuation per week and its severity. Moreover, several studies have demonstrated that constipation may precede the occurrence of motor symptoms underlying an earlier involvement of the enteric nervous system and the dorsal motor nucleus of the vagus in the α-synuclein pathology. In PD, constipation is mainly due to slower colonic transit or puborectalis dyssynergia, but the concomitant use of antiparkinsonian, pain, and antidepressant medications may worsen it. An accurate diagnosis and an adequate treatment of constipation it is pivotal to prevent complications such as intestinal occlusion and to ensure an optimal clinical response to levodopa.