Objective: Sleep prepares key neural structures for next-day learning, and sleep obtained after learning promotes subsequent memory consolidation supporting long-term retention. This study examined whether sleep the night before and after a therapy session predicts aspects of treatment adherence. Method: As part of a randomized clinical trial, 188 adults (62.7% female, mean age = 47.5, 80.5% Caucasian) with persistent insomnia received cognitive–behavioral therapy for insomnia. Patients completed a sleep diary before and after treatment sessions. Minutes spent awake during the night (total wake time; TWT) and total sleep time (TST) were used as measures of sleep disturbance. At each treatment session, therapists rated participant understanding of the session and homework compliance from the previous session. Results: Compared to longer TWT, before session shorter TWT was associated with increased treatment understanding the next day. After session shorter TWT was also associated with increased understanding, but not homework compliance the subsequent session compared to participants with longer TWT. Similar results were obtained for TST. Conclusions: Improving sleep may benefit patient adherence to treatment. Sleep may influence processes related to initial learning and subsequent consolidation of treatment information. Future studies should examine whether improved sleep within other psychiatric disorders is also an ingredient to the successful outcome of psychosocial interventions.