The purpose of the study was to determine the role of age and obesity in patients' rehabilitation needs following total hip arthroplasty (THA). The hypothesis was that older, obese patients would require subacute rehabilitation services more often than would their younger leaner counterparts. A retrospective study of 500 patients who underwent THA at the Hospital for Special Surgery was performed. Following surgery, the patients' functional performance was recorded daily on a valid and reliable THA functional milestone form. Variables chosen for analysis included patients' age, body mass index (BMI), performance on 4 functional milestones, and discharge status of healthy, overweight, obese, or morbidly obese based on the National Institute of Health guidelines. Forty-seven percent of patients were discharged from the acute care hospital to a subacute rehabilitation facility. These patients achieved fewer functional milestones, were older, and were more obese. The mean age of patients discharged to subacute rehabilitation facilities was 73.8 compared to the mean age of patients not needing subacute rehabilitation, 65.7 (P < .001). The mean BMI of patients requiring subacute rehabilitation was 28.8 compared to the mean BMI for those not needing subacute rehabilitation, 27.2 (P < .05). Achievement of functional milestones decreased as patients' age increased and obesity values approached obese and morbidly obese. As the number of older and more obese patients failing to achieve functional milestones rises, the number of discharge referrals to subacute rehabilitation facilities concomitantly increases. This finding provides a foundation for further research to investigate other factors affecting discharge disposition and may help in establishing standardized guidelines and predictors for determining the likelihood that a patient will need rehabilitation following THA.