Introduction: The international outcome inventory for hearing aids (IOI-HA) is a questionnaire widely used to assess the subjective benefits of hearing aids. This study aimed to evaluate the relationship between IOI-HA outcomes and target mismatch in real-ear measurement (REM). Methods: Thirty-four ears of 25 patients who had worn hearing aids were evaluated using the Korean version of the IOI-HA and REM after fi tting for 2 months. Real-ear insertion gain (REIG) was measured at three different levels of input intensity - 50, 65, and 80 dB sound pressure level (SPL) - and a frequency range of 0.25-6 kHz. Factors 1 and 2 and total IOI-HA scores were compared with the mismatches of REIGs and target gains of REM. Results: Factor 1, factor 2, and total IOI-HA scores were 14.6 +/- 3.5, 11.4 +/- 2.2, and 25.9 +/- 5.1, respectively. The averages of the difference of REIGs and target gains in REM at 50, 65, and 80 dB SPL input levels were - 3.1 +/- 6.7, - 2.3 +/- 7.2, and - 3.0 +/- 8.2, respectively. Factors 1 and 2 scores of the IOI-HA showed significant correlations with target mismatch in REM at 1 kHz and 0.75 kHz frequencies, respectively. Total IOI-HA scores had significant correlations with target mismatches in REM at 0.75 and 1 kHz frequencies. Conclusion: IOI-HA scores correlated with target mismatch in REM at mid frequencies. The IOI-HA can be a useful screening measure for evaluating the necessity of further adjustments in hearing aids through REM at mid frequencies.