The purpose of the current study was to examine the effects of cognitive behavior therapy (CBT-I) for insomnia on patients with insomnia co-morbid with hearing impairment. A randomized controlled design was used with a 3-month follow-up. Thirty-two patients with insomnia co-morbid with hearing impairment were randomized to either CBT-I or a waitlist condition (WLC). The primary outcome was insomnia severity. Secondary outcomes were sleep diary parameters, dysfunction, anxiety, and depression. Compared to WLC, CBT-I resulted in lower insomnia severity at post-treatment and at follow-up (d = 1.18–1.56). Relative to WLC, CBT-I also led, at both assessment points, to reduced total wake time (d = 1.39) and increased sleep restoration (d = 1.03–1.07) and sleep quality (d = 0.91–1.16). Both groups increased their total sleep time, but no significant group difference emerged. Compared to WLC, CBT-I resulted in higher function (d = 0.81–0.96) and lower anxiety (d = 1.29–1.30) at both assessment points. Neither CBT-I nor WLC led to improvement on depression. Based on the Insomnia Severity Index, more CBT-I (53–77%) than WLC participants (0–7%) were treatment responders. Also, more CBT-I (24%) than WLC participants (0%) remitted. In patients with insomnia co-morbid with hearing impairment, CBT-I was effective in decreasing insomnia severity, subjective sleep parameters, dysfunction, and anxiety. These findings are in line with previous results on the effects of CBT-I in other medical conditions.