Background/aim: Tinnitus is seen in 15% of the general population; in 1%-6% of this number, the quality of life is seriously affected by this chronic condition. Chemical, oxidative, and emotional stressors are important in terms of the clinical course of tinnitus. Apelin is an endogenous peptide which is an oxidative stress mediator. It has been shown that the apelin/APJ (apelin junction receptor) system plays various roles in the physiology and pathophysiology of many organs. However, the role of the apelin/APJ system as an oxidative stress mediator in tinnitus is unknown. We investigated the level of apelin in patients with normal hearing and bilateral tinnitus.Materials and methods: We enrolled patients diagnosed with bilateral idiopathic tinnitus. Tinnitus severity was determined using the tinnitus handicap inventory (THI). We recorded the levels of plasma apelin-13 and biochemical parameters.Results: The mean apelin level of the control group was higher than that of the patient group (P = 0.002). A significant negative correlation was evident between the apelin level and the THI (r = -0.460, P = 0.003). The triglyceride (TG) level was significantly higher in the patient group than in the control group (P