OBJECTIVE: To examine trajectories of recovery and change in patterns of personal care and instrumental functional activity performance to determine whether different assessment interval designs within a 12-month period yield different estimates of improvement and decline after acute hospitalization and inpatient rehabilitation. DESIGN: Secondary analysis of a 12-month prospective cohort study. SETTING: Transition to the community. PARTICIPANTS: Adults (N=419) admitted to acute care and receiving inpatient rehabilitation for a neurologic, lower-extremity musculoskeletal, or medically complex condition. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Improvement, no change, and decline as measured by the personal care and instrumental scale of the Activity Measure for Post-Acute Care. RESULTS: Assessment at the end of a single 12-month follow-up assessment interval showed that over 60% of the participants improved. In contrast, analysis of 2 fixed-length 6-month assessment intervals revealed an almost 40% decrease in the proportion who improved from 6 to 12 months. Fewer participants continued to improve in the time periods further from the acute hospitalization and the proportion of subjects who declined increased from 21.4% to 31.2% to 38.0% over the 3 consecutive assessment intervals (baseline to 1 mo, 1-6 mo, 6-12 mo). Only 58 (19.7%) participants continued on the same path of recovery from baseline to 12 months (9.8% improved over all 3 consecutive time periods, 3.1% made no change, 6.8% declined). CONCLUSIONS: Examination of change over shorter compared with longer assessment intervals revealed considerable variability in the trajectories of recovery. Research is needed to determine the appropriate frequency and timing for measuring and monitoring function and recovery after an acute hospitalization.