Objectives: To investigate the correlation between sleep disorders and the concentrations of three metals analyzed from hair samples of PD patients.The hypothesis of an involvement of an imbalance of metals in the development of Parkinson's Disease (PD) has been strengthened by several clinical chemistry studies. Interestingly, while sparse, some studies have correlated the imbalance of metals in PD patients with comorbidities present in this disease. Although not all PD sufferers present sleep disturbances, significant disorders of sleep are common in this population. Methods: Sleep evaluation was divided into three parameters: sleep quality, excessive daytime sleepiness and clinically probable REM Sleep Behavior Disorder. Flame atomic absorption spectrometry (F AAS) was used to assess the concentrations of calcium, iron and zinc in hair samples collected from a population of PD patients registered in a Brazilian city and from controls (a total of 53 subjects). All subjects lived within a restricted geographical region and were exposed to similar environmental conditions. Results: PD patients with poor sleep quality and excessive daytime sleepiness exhibited significant differences in concentrations of calcium, but not iron or zinc when compared to levels found in controls and PD patients who do not report these sleeping problems. Discussion: Our data suggest that different subgroups of PD patients exist, and clinical chemistry could be useful as a biomarker for these subgroups, which needs to be confirmed in a larger patient population. Further, our data raise the question regarding whether normalization of calcium levels could improve the sleep quality and somnolence in PD patients.