The authors have studied the consequences of resection of Hoffa's fat pad during total knee arthroplasty (TKA). Sixty eight patients undergoing primary TKA were randomised to have Hoffa's fat pad either resected or preserved. Biopsy specimens of Hoffa's fat pad were taken for pathological study in all patients. Radiological, functional and clinical evaluation was made after surgery, before discharge from hospital, after one month and after six months. Thirty six percent of the patients were found to present inflammatory infiltration of Hoffa's fat pad, and severe fibrosis was found in 33 %. A progressive decrease in postoperative anterior knee pain was found in 95% of the patients in both groups. Hoffa's fat pad resection did not appear to result in a change in patellar tendon length during the first six months after TKA. Preoperative fibrosis of Hoffa's fat pad may play a role in postoperative pain and range of motion.