Here, we describe the clinical characteristics of patients with Parkinson's disease, as well as study the relationship between sleep quality and cognitive functions. This is a descriptive-analytical cross-sectional study in which we evaluate episodes of depression and anxiety, as well as the state of general health, disease progression, sleepiness, sleep quality and cognitive functions of 24 patients with Parkinson's disease without dementia. We found a moderate inverse correlation between memory and sleep disturbances, and a moderate inverse correlation of memory and visuospatial function. We also observed other associations between subjective sleep quality and visuospatial function, sleep latency and the overall result of the SCOPA-COG, and between sleep duration and attention; all of these correlations were inverse and weak. This study suggests that mild cognitive deficits in the absence of dementia are associated with poor sleep quality.