This systematic review aimed to examine whether higher comorbidity burden, as assessed by comorbidity indices, was associated with a functional autonomy decline in individuals with cognitive impairment. The search was conducted in the following databases: PubMed/MEDLINE, ScienceDirect, Cochrane, and Embase. Both cross-sectional and longitudinal studies that examined the relationship between comorbidity indices and scales measuring activities of daily living (ADL) in individuals with cognitive impairment were included. The quality assessment tool for observational cohort and cross-sectional studies of the National Institutes of Health (NIH) was used. Overall, 12 studies were included, among which three were longitudinal. Significant association was frequently reported by cross-sectional designs (n=7 studies) and only one study reported a significant longitudinal association. This longitudinal study repeatedly assessed both comorbidity burden and functional autonomy, and considered comorbidity burden as a time-varying covariate. Considering comorbidity burden as a time varying covariate may deal with the dynamic nature of comorbidity burden over time, and conducting repeated assessments during the follow-up using both comorbidity index and ADL scales may increase their sensitivity to reliably measure comorbidity burden and functional autonomy decline over time. In conclusion, a higher comorbidity index was associated with a lower level of functional autonomy in people with cognitive impairment. This relationship seems to be dynamic over time and using comorbidity indices and ADL scales only once may not deal with the fluctuation of both comorbidity burden and functional autonomy decline. To cope with complexity of this relationship this review highlights some methodological approaches to be considered.