971 Treating acute insomnia using CBT-I—Ellis et al. INTRODUCTION Chronic insomnia is a significant public health concern and has been linked to the development and/or worsening of a number of physical and psychiatric conditions.1–6 At symptom level, between 30–48% of the population report having chronic insomnia and at syndrome level the prevalence, albeit significantly lower at between 6–15%, still represents a major challenge at both individual and societal levels.7,8 Importantly, chronic insomnia is also a persistent disorder with one study demonstrating the majority (74%) of individuals reporting insomnia at baseline still report having insomnia 1 y later and almost half (46%) report having insomnia at three consecutive annual assessment points.9 In essence, chronic insomnia is a highly prevalent, costly (the direct costs of chronic insomnia alone are estimated to be in the region of $13.9 billion annually),10 and largely unrelenting condition. Standard Cognitive Behavioral Therapy for Insomnia (CBT-I), a 6to 8-w intervention targeting sleep-incompatible thoughts, beliefs, and behaviors, has been consistently Study Objectives: Despite considerable evidence supporting cognitive behavioral therapy for insomnia (CBT-I) for chronic insomnia, it remains untested within the context of acute insomnia. This study examined the efficacy of a single session of CBT-I, with an accompanying self-help pamphlet, for individuals with acute insomnia. Design: A pragmatic parallel group randomized controlled trial. Setting: Community. Participants: Forty adults (mean age 32.9 ± 13.72 y) with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) defined insomnia disorder, except a self-reported duration of less than 3 mo (i.e., acute insomnia), who reported no previous exposure to CBT-I and were not currently taking medication for sleep. Interventions: A single 60to 70-min session of CBT-I (n = 20), with an accompanying self-help pamphlet, or wait list control group (n = 20). All subjects were offered a full individual course of CBT-I on completion of the study, regardless of group allocation. Measurements and Results: Subjects completed sleep diaries and the Insomnia Severity Index (ISI) pretreatment and 1 mo following treatment. There were no between-group differences on baseline ISI scores or subjective sleep continuity. The intervention group reported significantly lower ISI scores than controls (t(38) 2.24, P < 0.05) at follow-up. Further, using proposed ISI scores for identifying insomnia caseness (i.e., ≥ 10), 60% of those in the CBT-I group had remitted by 1 mo compared to 15% of those in the control group. Conclusions: This single session of cognitive behavioral therapy for insomnia (CBT-I) is sufficiently efficacious for a significant proportion of those with acute insomnia. The results are discussed in terms of integrating this brief form of CBT-I into the “stepped care” model of insomnia. Trial Registration: Testing the efficacy of an early intervention for acute insomnia (SRCTN05891695) http://www.controlled-trials.com/ ISRCTN05891695.