Background: Tinnitus is defined as a subjective auditory phantom phenomenon in which patients hear internal sounds when there is no external source of acoustic stimuli. Tinnitus is a result of a chain of plastic changes which have an effect on the entire auditory system. The aim of this study is to assess the cognitive function in patients with chronic idiopathic tinnitus.Methods: This case-control study included two groups: The control group (32 normal hearing individuals without tinnitus), the study group (32 normal hearing individuals with tinnitus). All individuals in the study had undergone full history taking, full otological examination, basic audiological evaluation, Arabic version of tinnitus handicap inventory (THI), Arabic version of Beck anxiety inventory (BAI), Arabic version of Montreal cognitive Assessment (MoCA) and electrophysiological tests (P300 and MMN). Results: No significant differences were found between the two groups as regards age and sex distribution. Patients with tinnitus had statically significant delayed P300 latencies compared to the control group. No significant differences were found regarding P300 amplitude, MMN amplitude and latency between the studied groups. In the tinnitus group, there were significant positive correlations between THI scores and both BAI scores and P300 latencies (P value <0.05) and significant positive correlations between P300 latencies and BAI scores (correlation coefficient r=0.87, P value = 0.000) while significant negative correlations between P300 latencies and MoCA scores (correlation coefficient r=-0.78, P value= 0.000) were noted.Conclusion: Tinnitus patients have impaired cognitive functions which are correlated to the severity of tinnitus and the degree of anxiety. The P300 test can be a useful test for objective evaluation of patients with tinnitus and to assess the cognitive function of tinnitus patients.