The purpose of our study was to determine the prevalence of frailty in Parkinson's disease (PD) patients and the relationship between individual frailty criteria and the severity of PD. We measured the five components of frailty (Fried et al.) and the severity of PD (unified Parkinson's disease rating scale (UPDRS)) in 50 optimally treated PD patients. Frailty was more prevalent in PD patients. While UPDRS scores differed between frail and non-frail participants (44.8+/-15.8 vs. 31.4+/-12.7, P<0.002), higher scores were not indicative of frailty. Weekly caloric expenditure best predicted frailty status (OR=22.0 [4.5,107.8]). Frailty and PD bear distinct therapeutic and prognostic significance; however, their clinical picture may overlap and screening PD patients for frailty may be warranted.