Little is known about the course of depressive symptoms in Parkinson's disease (PD). We studied the course of clinically significant depressive symptoms using data from two clinical trials that followed 413 early, untreated PD subjects for 12 to 18 months. We measured depressive symptoms with the 15-item geriatric depression scale (GDS-15); a score of > or =5 indicates clinically significant depressive symptoms. We used a time-dependent Cox model to examine the association between demographic variables, PD severity, and medication use on the time to resolution of depressive symptoms. One hundred fourteen of 413 (27.6%) subjects were screened positive for depression during the study, with a median GDS-15 score of 6, indicating mild symptoms. Within 6 months, 47% of subjects experienced remission of clinically significant depressive symptoms. Subjects with mild depressive symptoms were more likely to develop moderate to severe depressive symptoms (GDS > or = 10) than those without prior symptoms (relative risk = 6.16). Increasing severity of depressive symptoms, older age, and longer PD duration predicted a lower likelihood of symptom resolution (hazard ratios 0.83-0.92). Mild depressive symptoms have a variable course, with remission and development of more sustained and severe symptoms occurring over time. More severe depressive symptoms may herald a protracted course.