Parkinson's disease (PD) is a neurodegenerative disorder involving decreased dopamine release and atrophy of dopaminergic neurons of the substantia nigra. Frailty syndrome (FS) is common in older adults, which, in combination with PD symptoms, can substantially affect the quality of life (QOL). This study aimed to assess the prevalence of FS among PD patients and to identify variables affecting their QOL with particular attention to FS. The study included 296 patients (n = 173 women) with a mean age of 70.3 ± 5.7 years suffering from PD for an average of 8.2 ± 5.6 years. Patients were classified as at least stage II according to the Hoehn and Yahr scale. The following standardized questionnaires were used in the study: Schwab and England Activities of Daily Living (SE-ADL), Parkinson's Disease Questionnaire (PDQ-39), Beck Depression Inventory (BDI), Unified Parkinson's Disease Rating Scale (UPDRS), and Tilburg Frailty Indicator (TFI). FS was found in 96% (n = 283) of the PD patients studied. No depression occurred in 30% (n = 89) of subjects, moderate depression in 48% (n = 141) of subjects, and severe depression in 22% (n = 66) of subjects. The mean score of the PDQ-39 questionnaire in PD subjects with FS was 41.6 pts (min-max: 5.2-81.5 pts; SD = 17.4 pts), which was statistically significantly higher than in subjects without FS (p < 0.05). FS has been shown to be present in most of the subjects with PD. FS occurs more frequently with a longer PD period, which is associated with reduced physical capacity and QOL. Physical activity improves QOL and reduces disease progression. FS, similar to PD, is a common cause of disability in older adults and their dependency. Predictors such as depression, advanced stage of the disease, higher education, and low professional and economic status significantly affect the QOL level of PD patients. However, the results obtained among the Polish population of PD patients do not confirm the impact of FS on the QOL, so there is a need to conduct further research on this subject.