Objective: Intra-articular glucocorticoid (IAGC) injection treatment is an easy and effective way to treat the signs and symptoms of arthritis, but there is limited knowledge on the adequate dosing for different joints. The aim of this study was to compare the outcome between two common doses of intra-articular triamcinolone hexacetonide (THA) for knee synovitis using the relapse rate during 6 months.Methods: A total of 159 adult patients with rheumatoid arthritis (RA) or psoriatic arthritis (PsA) and active knee synovitis were randomized to IAGC injection with 20 mg or 40 mg THA. Participants were blinded to the treatment dose. The primary endpoint was relapse of arthritis. When symptoms from the treated joint recurred and signs of arthritis could be confirmed on a subsequent clinical examination, a relapse was recorded and the duration of response survival was calculated. At the end of the observation period, patients without relapse were telephoned to verify the persistence of the good treatment response.Results: The proportion of relapse after 6 months was equal in the 20 mg and 40 mg THA treatment arms (30% vs 32%, respectively, p = 0.822), and no significant differences were found in the subgroups with RA and PsA patients.Conclusion: As no difference in outcome was found between the compared doses, the lower 20 mg THA dose should be preferred in IAGC treatment for knee synovitis in chronic polyarthritis. This may also reduce pharmaceutical costs and metabolic side effects.EudraCT number: 2014-000993-20, Clinical Trials.gov identifier: NCT02437461