The purpose of this study was to investigate the effects of cognitive behavioral therapy for insomnia (CBTI) in patients with Restless Legs Syndrome (RLS). This is a randomized controlled study. The patients were sequentially selected and randomly assigned to either a CBTI group or a non-CBTI group. A total of 25 RLS patients with comorbid insomnia were recruited from a tertiary university hospital sleep center. Twelve were assigned to the CBTI group, and 13 were assigned to the non-CBTI group. The CBTI group received 4 sessions of behavioral therapy, while the non-CBTI group received one informative session on sleep hygiene. All patients completed sleep and psychiatric-related questionnaires. In addition, each individual completed a one-week sleep log for collecting subjective sleep data and actigraphy for objective sleep data. After conducting the CBTI, there were significant improvements in severity of insomnia symptoms, subjective sleep efficiency, total sleep time, latency to sleep onset, wake after sleep onset, objective latency to sleep onset, and anxiety in the CBTI group as compared to the non-CBTI group. The effect of CBTI on sleep-related data was maintained for up to three months. CBTI was effective in RLS patients by improving sleep quality and anxiety symptoms. CBTI may be considered in clinical practice for RLS patients with comorbid insomnia. Copyright © 2020 Elsevier B.V. All rights reserved.