OBJECTIVE: To evaluate data reporting related to external validity from randomized controlled trials (RCTs) assessing pharmacologic and nonpharmacologic treatment for hip and knee osteoarthritis (OA). METHODS: All RCTs assessing pharmacologic treatments and nonpharmacologic treatments for hip and knee OA indexed between January 2002 and December 2006 were selected. A sample of 120 articles were randomly selected: 30 each assessing pharmacologic treatments, surgery or technical interventions, rehabilitation, and nonimplantable devices. RESULTS: The country was clearly reported in 25 (21%) reports, the setting described in 40 (33%) reports, and the number of centers in 54 (45%). Details about the centers (volume of care) were given in 24 (20%) reports. Rates were lower for surgical trials for the country (3%), the setting (3%), the number of centers (13%), and details about the centers (7%). The intervention was adequately described in all pharmacologic reports and in >80% of rehabilitation reports. The technical procedure was given in all surgical intervention trial reports, but the type of anesthesia was reported in 4 (13%), preoperative care in 2 (7%), and postoperative care in 15 (50%). The device was described in 93% of device trial reports, but the manufacturer was reported in only 33%. CONCLUSION: There is low reporting of data related to external validity in reports of RCTs assessing pharmacologic and nonpharmacologic treatments for hip and knee OA.