Sleep disturbances are common and often severe in patients with Parkinson's disease (PD) and their symptoms can be present at any time of day. The purpose of our study was to examine how excessive daytime sleepiness or poor nocturnal sleep quality and mood disorders influence the quality of life (QoL) in PD patients. Ninety-three PD patients from eastern Slovakia were recruited (49.5% males, mean age 68.0 ± 9.5 years, mean disease duration 6.1 ± 5.9 years). Sleep disturbances were measured using the Epworth Sleepiness Scale (ESS) and the Pittsburgh Sleep Quality Index (PSQI); QoL with the Parkinson's Disease Quality of Life Questionnaire (PDQ-39); depression and anxiety with the Hospital Anxiety and Depression Scale (HADS) and disease severity with the Unified Parkinson's Disease Rating Scale (UPDRS). χ2 test, bivariate correlations and multiple linear regressions were performed. PSQI and ESS had significant correlations with worse QoL (p < 0.01, p < 0.05, respectively). HADS-D (p < 0.01), HADS-A (p < 0.01), UPDRS (p < 0.01) and disease duration (p < 0.05) were also significantly related to worse QoL. In the linear regression analysis, however, only PSQI (p < 0.01), anxiety (p < 0.001) and UPDRS (p < 0.001) remained significant. The model with PSQI explained 74% of the variance, and the model with ESS explained 63% of the variance in PDQ-39 when analyses were performed separately. In an overall model, however, only PSQI remained significant, accounting for 82% of the variance in PDQ-39. Nighttime poor sleep and anxiety are important contributors leading to a worse QoL. As these are treatable conditions, they should be recognized by clinicians and managed properly.