The objective of this study is to assess how the non-motor symptoms of Parkinson's disease (PD), such as depression, cognitive deterioration, neuropsychiatric and sleep disorders, affect the quality of life, and to compare them with the motor symptoms in order to determine their real impact. A cross-sectional study was designed including 99 patients (mean age 68.5 ± 9.9 years, duration of disease 8.7 ± 6.2 years). Demographic data, onset of PD, years on treatment with levodopa (LD), class of dopaminergic drug prescribed, and dosages were obtained. The following scales were used: quality of life (PDQ-39), Unified Parkinson's Disease Rating Scale (UPDRS I-IV), Parkinson Disease Sleep Scale (PDSS) and daytime sleepiness (Epworth), Mini-Mental State Examination, depression (HAM-D), and the neuropsychiatric inventory (NPI-10). The PDQ-39 summary index (PDQ-39 SI) was 24.7 ± 13.2. A linear regression model including all variables showed that four independent variables accounted for 67.2% of the variance in the PDQ-39 SI (F = 33,277; p < 0.001): NPI, PDSS, UPDRS IV, and UPDRS I. When sub-items of the NPI, PDSS and UPDRS IV scales are analyzed, significant correlations (p < 0.001) are found between the PDQ-39 SI and depression, agitation, apathy, anxiety, hallucinations, delusions, incontinence of urine, morning painful posturing, restlessness in bed, morning fatigue, duration of off periods, unpredictable and predictable off periods, early morning dystonia, and sudden off periods. Neuropsychiatric symptoms, especially depression, nighttime sleep disorders such as urinary incontinence, nighttime restlessness, morning fatigue and somnolence, off-period dystonia and motor fluctuations are the variables that most affect the quality of life of patients with PD.