Idiopathic Parkinson's disease (IPD) is characterized by motor signs such as akinesia, rigidity, and often tremor at rest. In addition to these symptoms, depression is a common finding affecting 40% of patients with IPD. This study evaluates the effect of the selective serotonin reuptake inhibitor, citalopram, on motor and nonmotor symptoms of depressed and nondepressed patients with IPD. Forty-six nondemented patients with IPD (24 men, 22 women; mean age 64 +/- 5.3 years; mean +/- SD disease duration, 6.4 +/- 3.2 years; mean +/- SD Hoehn-Yahr stage, 2.8 +/- 1.2) were included in the study. Patients were divided in two subgroups: depressed (n = 18) and nondepressed (n = 28). Citalopram was added in an unblinded manner, starting with 10 mg/d, and, after a week, increased up to 20 mg/d in the depressed subgroup (n = 18) and in half of the nondepressed subgroup (n = 14). Parkinsonian and depressive symptoms were evaluated before and after 1 and 4 months of treatment. Statistical evaluation was made by analysis of variance for repeated measures. Citalopram did not worsen motor performance in IPD, but improved bradykinesia and finger taps after 1 month and 4 months of treatment both in patients with and without depression (p < 0.05 versus baseline). A clear improvement in mood was also observed in 15 of 16 patients with depression. Although case reports indicate that citalopram can potentially worsen the motor symptoms in patients with PD, to date this effect has not been confirmed. Many of the symptoms, typically associated with depression, can be observed in nondepressed patients with IPD, because signs thought to represent depression can be produced by Parkinson's disease. In this study, we observed that when combined with levodopa, citalopram induces an improvement of motor performance, in particular of subscores 23 and 31 of Unified Parkinson's Disease Rating Scale both in depressed and in nondepressed patients with IPD.