Very few studies have focused on patient characteristics that influence length of stay (LOS) in fast-track total hip (THR) and knee arthroplasty (TKR). The aim of this prospective study was to identify patient characteristics associated with LOS and patient satisfaction after total hip and knee replacement surgery. Between September 2003 and December 2005, 712 consecutive, unselected patients (440 women) with a mean age of 69 (31-91) years were admitted for hip and knee replacement surgery at our specialized fast-track joint replacement unit. Epidemiological, physical, and perioperative parameters were registered and correlated to LOS and patient satisfaction. 92% of the patients were discharged directly to their homes within 5 days, and 41% were discharged within 3 days. Age, sex, marital status, co-morbidity, preoperative use of walking aids, pre- and postoperative hemoglobin levels, the need for blood transfusion, ASA score, and time between surgery and mobilization, were all found to influence postoperative outcome in general, and LOS and patient satisfaction in particular. We identified several patient characteristics that influence postoperative outcome, LOS, and patient satisfaction in our series of consecutive fast-track joint replacement patients, enabling further attention to be paid to certain aspects of surgery and rehabilitation.