Objective: To evaluate the efficacy of a brief 4-w group-administered treatment program of cognitive behavior therapy for insomnia (CBT-I) for older adults with sleep maintenance insomnia. Design: Randomized controlled trial of CBT-I compared to waitlist control with comparisons at pretreatment, posttreatment, and 3-mo follow-up. Setting: Flinders University Sleep and Circadian Rhythm Research Laboratory, Adelaide, South Australia. Participants: One-hundred eighteen adults with sleep maintenance insomnia (mean age = 63.76 y, standard deviation = 6.45 y, male = 55). Interventions: A 4-w, group-based treatment program of CBT-I including bedtime restriction therapy, sleep education, and cognitive restructuring. Measurements: Seven-day sleep diaries, actigraphy, and several self-report measures to assess perceived insomnia severity, daytime functioning, and confidence in and beliefs about sleep. Results: The brief group-administered CBT-I program produced improvements in the timing and quality of sleep including later bedtimes, earlier out-of-bed times, reduced wake after sleep onset, and improved sleep efficiency. Participants also reported a reduction of the Insomnia Severity Index, Flinders Fatigue Scale, Epworth Sleepiness Scale, Daytime Feeling and Functioning Scale, Sleep Anticipatory Anxiety Questionnaire, the Dysfunctional Beliefs and Attitudes Scale, and increased Sleep Self-Efficacy Scale. Conclusions: The treatment program used in the current study has demonstrated potential for a brief, inexpensive, and effective treatment of sleep maintenance insomnia in the older adult population.