Patients affected by osteoarthritis totalling 358 (142 males and 216 females) were recruited in an open study which lasted up to three months. All patients started treatment with etodolac 600 mg/die per os. 74 patients were treated and followed for 15 days, 94 for one month, 54 for two months, and 132 for three months. Clinical evaluations, performed at baseline and after 15, 30, 60, and 90 days of treatment were made on the following parameters: intensity of pain, index of sleep disturbance caused by symptoms related to osteoarthritis, investigator's evaluation of the global patient's condition, patient's self-evaluation about his own condition, presence and duration of morning stiffness, presence and duration of stiffness at rest, and finally the investigator's integrated evaluation about the effectiveness tolerance of etodolac during the study. All the parameters showed a noticeable and significant improvement in all groups of patients, stratified by sex, age, and duration of the disease. The younger patients and those patients with osteoarthritis of a less prolonged duration achieved the best results. Only slight differences were registered by examining the baseline values of the various parameters or the extent of the different improvements achieved, on the basis of sex, and duration of osteoarthritis and the non-steroidal anti-inflammatory drugs previously used. Among the 27 patients who withdrew, eight dropped out for clinical inefficacy and 15 for intolerance. In all these latter cases a prompt and complete resolution of the adverse reaction was achieved and maintained after the interruption of therapy. In the 49 patients who presented side-effects, these were almost always related to the gastrointestinal tract and of slight intensity. A complete resolution was promptly achieved in 25 cases, while in 17 other patients the side-effect persisted during the course of the study, but it was considered not worthy of the patient dropping out. The profile of routine laboratory parameters, measured both at inception and at the end of the study, did not show relevant changes after treatment with etodolac. In conclusion this study demonstrated that etodolac is effective and well tolerated in the prolonged treatment of patients with active osteoarthritis.