OBJECTIVES: Patients with unilateral hearing loss (UHL) have difficulty in recognizing the direction of a sound. Previous studies have shown that hearing aids (HAs) could improve the directional perception of sound. In this study, we analyzed the results of sound localization tests in patients using a unilateral HA. METHODS: All patients with UHL who had performed sound localization tests since 2018 were included in this study. Sound localization tests, functional gain tests, and the speech discrimination scores (SDSs) were analyzed. The tests were obtained at 1-, 3-, and 6-month after fitting the HA. RESULTS: Of the 32 patients with UHL, 13 were right-sided and 19 were left-sided. After 6 months of using a HA, the results of the sound localization test were significantly better in patients with right than left UHL (percent correct [PCT], 61.9 +/- 24.0% vs. 37.9 +/- 24.6%, p = .011; mean absolute error (MAE), 41.4 +/- 23.9 degrees vs. 65.5 +/- 28.6 degrees , p = .018; root-mean-square error (RMS), 25.8 +/- 17.6 degrees vs. 48.8 +/- 24.5 degrees , p = .007]. The aided SDSs were not different between the two groups (78.7 +/- 16.5% vs. 77.2 +/- 18.5%, p = .825). CONCLUSION: The side of the hearing loss could have a substantial effect on sound localization in UHL patients using a HA. Sound localization test results should be interpreted with the consideration of this discordance. LEVEL OF EVIDENCE: 4.