Behavioural disturbances are frequently observed in Parkinson's disease (PD), including mood and anxiety disorders. The existence of a comorbidity between such psychiatric disorders in PD patients has been suggested only in a few studies. To assess the prevalence of mood and anxiety disturbances, and the rate of comorbidity of such disorders in PD. Secondary aim was to correlate the prevalence of psychiatric disorders in PD with age, sex, laterality of motor symptomatology, clinical features, severity of disease, age of onset and PD duration, and anti-parkinsonian therapy. Ninety consecutive PD outpatients, and 90 age- and sex-matched controls were included. All PD patients enrolled were non-fluctuating (21 de novo, 69 treated with levodopa or dopamine agonists). PD patients and controls with Mini Mental State Examination score <23 were excluded. Psychiatric diagnosis was performed by semistructured interview according with DSM-IV criteria and the severity of depressive and anxious symptoms was rated with clinical rating scales. Major depression was found in 21.1% PD patients vs. 3.3% controls (P < 0.01, chi-square analysis), dystimia in 18.8% PD patients vs. 4.4% controls (P < 0.05), panic disorders in 30% PD patients vs. 5.5% controls (P < 0.01). No difference in the prevalence of other anxiety disorders was observed between the two groups. The comorbidity of mood and anxiety disorders was found in 19.3% PD patients vs. 8.6% controls (P < 0.01). No correlation was reported between the prevalence of behavioural disturbances and any of the demographic, clinical or pharmacological data taken into account. Our findings might suggest the existence of a wide spectrum of psychiatric disorders in PD ranging from pure depressive disorders, comorbid depressive and anxiety disorders, and pure anxiety disorders, presumably linked to the same neurobiological substrate.