The efficacy and safety of nabumetone were evaluated in short term (up to 6 months), double blind, comparative trials and a longterm (up to 8 years), open label, noncomparative trial. In the short term trials, nabumetone was determined to be significantly more effective than placebo and as effective as naproxen and aspirin. The most common adverse effects that occurred were related to the gastrointestinal tract, nervous system, skin, and special senses. In the longterm trial, nabumetone was effective in 62% of patients, without complicating effects, for at least 1 year. This beneficial response was maintained in a fair percentage of patients for up to 5 years or more. The average treatment duration before withdrawal was at least 1.1 years. Therefore, most patients in the longterm trials experienced a beneficial response for a significant duration of therapy.