Objective:To investigate acclimatization to hearing aids.Design:Forty-eight subjects took part in a study in which hearing aid benefit was measured four times over the initial 3 mo of participation. At the start, 24 subjects were experienced hearing aid users and 24 had never worn a hearing aid before. Subjects wore one of three models of hearing aid with one of six different configurations (combination of frequency response and method of output limiting). Hearing aid benefit was measured with CID W-1 spondees and the Hearing in Noise Test (HINT) test. Testing took place on Days 0 (day of fitting), 30, 60, and 90. Analyses of variance were used to determine whether hearing aid benefit changed over time as a function of hearing aid user status, hearing aid configuration, and hearing aid volume setting.Results:There were small, nonsignificant changes in hearing aid benefit over the test sessions with both sets of test materials. There were no interactions between hearing aid benefit over time and hearing aid user status or hearing aid volume setting. There was an interaction between benefit over time and hearing aid configuration on one test measure only.Conclusions:The data showed little evidence of acclimatization over the 3 mo of hearing aid use. The test materials used here were low- to mid-frequency sensitive, and, therefore, it is concluded that if acclimatization did occur, it did so primarily at high frequencies. Because the HINT test has good face validity to everyday listening situations, it is suggested that the clinical ramifications of acclimatization are probably small.