Objective:To identify the factors associated with functional status decline in intensive care unit patients.Methods:In this prospective study, patients in an intensive care unit aged 18 years or older without neurological disease or contraindications to mobilization were included. The exclusion criteria were patients who spent fewer than 4 days in the intensive care unit or died during the study period. Accelerometry was used to assess the physical activity level of patients. We recorded age, SAPS 3, days on mechanical ventilation, drugs used, comorbidities, and functional status after intensive care unit discharge. After intensive care unit discharge, the patients were assigned to a dependent group or an independent group according to their Barthel index. Logistic regression and the odds ratio were used in the analyses.Results:Sixty-three out of 112 included patients were assigned to the dependent group. The median Charlson comorbidity index was 3 (2 - 4). The mean SAPS 3 score was 53 ± 11. The patients spent 94 ± 4% of the time spent in inactivity and 4.8 ± 3.7% in light activities. The odds ratio showed that age (OR = 1.08; 95%CI 1.04 - 1.13) and time spent in inactivity (OR = 1.38; 95%CI 1.14 - 1.67) were factors associated with functional status decline. Time spent in light activity was associated with a better functional status (OR = 0.73; 95%CI 0.60 - 0.89).Conclusions:Age and time spent in inactivity during intensive care unit stay are associated with functional status decline. On the other hand, performing light activities seems to preserve the functional status of patients.