Background Promotion of increased physical activity is advocated for survivors of an intensive care unit (ICU) admission to improve physical function and health-related quality of life. Objective The primary aims of this study were: (1) to measure free-living physical activity levels and (2) to correlate the measurements with scores on a self-reported activity questionnaire. A secondary aim was to explore factors associated with physical activity levels. Design This was a prospective cohort study. Methods Nested within a larger randomized controlled trial, participants were block randomized to measure free-living physical activity levels. Included participants wore an accelerometer for 7 days during waking hours at 2 months after ICU discharge. At completion of the 7 days of monitoring, participants were interviewed using the Physical Activity Scale for the Elderly (PASE) questionnaire. Factors associated with physical activity were explored using regression analysis. Results The ICU survivors (median age=59 years, interquartile range=49–66; mean Acute Physiologic Chronic Health Evaluation [APACHE II] score=18, interquartile range=16–21) were inactive when quantitatively measured at 2 months after hospital discharge. Participants spent an average of 90% of the time inactive and only 3% of the time walking. Only 37% of the sample spent 30 minutes or more per day in the locomotion category (more than 20 steps in a row). Activity reported using the PASE questionnaire was lower than that reported in adults who were healthy. The PASE scores correlated only fairly with activity measured by steps per day. The presence of comorbidities explained one third of the variance in physical activity levels. Limitations Accelerometer overreading, patient heterogeneity, selection bias, and sample size not reached were limitations of the study. Conclusions Survivors of an ICU admission greater than 5 days demonstrated high levels of inactivity for prolonged periods at 2 months after ICU discharge, and the majority did not meet international recommendations regarding physical activity. Comorbidity appears to be a promising factor associated with activity levels.