Comorbidity is frequent in Parkinson´s disease (PD) patients and increases significantly over time. Comorbidity predicts mortality in PD patients over time independently of the effects of other factors. Comorbidity seems to be higher in PD patients than in controls but equivalent to Alzheimer´s disease (AD) patients. Polypharmacy is more frequent in PD and AD patients than in controls. Total number of non-antiparkinsonian drugs could be used as a surrogate marker of comorbidity in PD patients.