Objectives: To determine the number of steps taken by older patients in hospital and 1 week after discharge; to identify factors associated with step numbers after discharge; and to examine the association between functional decline and step numbers after discharge. Design: Prospective observational cohort study conducted in 2015e2017. Setting and Participants: Older adults (!70 years of age) acutely hospitalized for at least 48 hours at internal, cardiology, or geriatric wards in 6 Dutch hospitals. Methods: Steps were counted using the Fitbit Flex accelerometer during hospitalization and 1 week after discharge. Demographic, somatic, physical, and psychosocial factors were assessed during hospitalization. Functional decline was determined 1 month after discharge using the Katz activities of daily living index. Results: The analytic sample included 188 participants [mean age (standard deviation) 79.1 (6.7)]. One month postdischarge, 33 out of 174 participants (19%) experienced functional decline. The median number of steps was 656 [interquartile range (IQR), 250e1146] at the last day of hospitalization. This increased to 1750 (IQR 675e4114) steps 1 day postdischarge, and to 1997 (IQR 938e4098) steps 7 days postdischarge. Age [b ¼ À57.93; 95% confidence interval (CI) À111.15 to À4.71], physical performance (b ¼ 224.95; 95% CI 117.79e332.11), and steps in hospital (b ¼ 0.76; 95% CI 0.46e1.06) were associated with steps postdischarge. There was a significant association between step numbers after discharge and functional decline 1 month after discharge (b ¼ À1400; 95% CI e2380 to À420; P ¼ .005). Conclusions and Implications: Among acutely hospitalized older adults, step numbers double 1 day postdischarge, indicating that their capacity is underutilized during hospitalization. Physical performance and physical activity during hospitalization are key to increasing the number of steps