Summary The aim of this study was to assess the effectiveness of Intensive Sleep Retraining, a novel, short duration behavioural therapy in treating chronic primary insomnia. Seventeen consecutive volunteers from the general public (mean age = 39.1 years), meeting selection criteria for chronic primary insomnia participated in the treatment study. The study was performed as a case replication series. Assessment involved sleep diary, actigraph and questionnaire measures of sleep and daytime functioning for a period of 2 weeks prior to, immediately after, and 6 weeks following the treatment. Treatment involved a single night of sleep deprivation, facilitating short sleep latencies (mean: 6.9 min) to a series of 50 brief nap opportunities. Following treatment, Sleep Onset Latency significantly decreased by a mean of 30.5 min (SD = 28.3), Wake Time after Sleep Onset significantly decreased by a mean of 28 min (SD = 34.0), and Total Sleep Time significantly increased by 64.6 min (SD = 45.5). Significant improvements were also seen in the daytime functioning and psychological measures of fatigue and vigour, cognitive sleep anticipatory anxiety and self-efficacy for sleep. This brief therapy was effective in improving sleep and some daytime functioning and psychological questionnaire measures. These improvements were maintained up to 2 months following the treatment weekend. Further exploration of this brief therapy is needed, with larger, randomized, placebo-controlled trials over longer follow-up periods, and in comparison to other traditional therapies for insomnia.