Introduction: Parkinson's disease is a multisystem disorder which is characterized by a combination of motor and non-motor symptoms. Non-motor symptoms include: depression, cognitive impairment, autonomic and sensor symptoms. It is difficult to detect and treat depression symptoms in patients with Parkinson's disease with dementia. Early identification and treatment of depression symptoms can greatly improve the quality of life in these patients, as well as facilitate the quality of caregivers' lives. Goal of the paper: The aim of our research was to evaluate frequency of depression occurrence in patients with Parkinson's disease with cognitive impairment. Patients and methods: We did a prospective study which included 59 PD patients, who came for a regular check-up to Neurological infirmary of the General Hospital in Niksic, in the interval from 1st January 2016to 31st December 2016, all of whom were previously diagnosed with Parkinson's disease. We tested their cognitive status using the Mini Mental State Examination scale. Out of 59 patients, 32 displayed cognitive deficit and were included in further research. We gave directions about testing to guardians or caregivers of the patients who displayed moderate or distinct cognitive impairment. The testing was done on the next check-up, with Cornell's depression scale. Results: Research showed that out of 32 patients, 5 (15.6%) didn't suffer from depression, 8 (25%) probably suffered from major depression, while 19 (59.4%) definitely suffered from major depression. On the cognitive scale, 6 (18.8%) patients had mild, 11 (34.4%) moderate and 15 (46.9%) distinct cognitive deficit. Out of 8 patients with probable depression 3 (9.4%) had mild, 3 (9.4%) had moderate and 2 (6.2%) distinct cognitive deficit. We can also: conclude that out of 19 (59.4%) with certain depression, 1 (3.1%) had mild, 5 (15.6%) had medium severe, and 13 (40.6%) had severe cognitive deficit. Conclusion: Prevalence of depression and dementia in Parkinson's diseasepatients is high. Our patients have moderate cognitive deficit in 34.4% of the cases, and distinct cognitive deficit in 46.9% of the cases; while 59.4% definitely suffers from major depression at some point of their illness. Their early detection is of great importance for treatment and quality of life of these patients.