In an increasingly aged population, sleep disturbances and neurodegenerative disorders have become a major public health concern. Poor sleep quality and cognitive changes are complex health problems in aging populations that are likely to be associated with increased frailty, morbidity, and mortality, and to be potential risk factors for further cognitive impairment. We aimed to evaluate whether sleep quality and excessive daytime sleepiness may be considered as early predictors of cognitive impairment. Study Objectives The objective of this study was to examine whether subjective sleep quality and daytime sleepiness are associated with cognition in middle-aged males. Participants A total of 189 healthy males born in 1953 were considered as participants for the study. Based on previous cognitive assessments, the participants were selected for the study as cognitively improved (N = 97) or cognitively impaired (N = 92). Methods The Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale measured subjective sleep quality and daytime sleepiness, respectively. Depressive symptoms were determined using Beck's Depression Inventory (BDI-II). A neuropsychological battery was administered to confirm group differences in cognitive functioning at the time when sleep data were collected. Results Compared with cognitively improved males, the cognitively impaired group reported significantly lower subjective sleep quality (5.40 ± 3.81 vs. 4.39 ± 2.40, p = 0.03). Forty-one percent of the sample exhibited poor sleep quality and 15% experienced excessive daytime sleepiness. There were few correlations between sleep parameters and cognitive test performance in the combined sample. Conclusion Self-reported poor sleep quality was related to cognitive changes, whereas daytime sleepiness was not related. Our results suggest that sleep quality may be an early marker of cognitive decline in midlife.