OBJECTIVE: To ascertain the effectiveness of clinical pathways for improving patient outcomes and decreasing lengths of stay after hip and knee arthroplasty. DESIGN AND SETTING: Twelve-month randomised prospective trial comparing patients treated through a clinical pathway with those treated by an established standard of care at a single tertiary referral university hospital. PARTICIPANTS: 163 patients (56 men and 107 women; mean age, 66 years) undergoing primary hip or knee arthroplasty, and randomly allocated to the clinical pathway (92 patients) and the control group (71 patients). MAIN OUTCOME MEASURES: Time to sitting out of bed and walking; rates of complications and readmissions; match to planned discharge destination; and length of hospital stay. RESULTS: Clinical pathway patients had a shorter mean length of stay (P = 0.011), earlier ambulation (P = 0.001), a lower readmission rate (P = 0.06) and closer matching of discharge destination. There were beneficial effects of attending patient seminars and preadmission clinics for both pathway and control patients. CONCLUSION: Clinical pathway is an effective method of improving patient outcomes and decreasing length of stay following hip and knee arthroplasty.