This study examined the long-term effects of a brief behavioral intervention for sleep improvement. The program was designed as a complete self-help approach by correspondence, and consisted of self-assessments of sleep-related behavior, target-setting for behavior change, an educational booklet, self-monitoring of the behaviors for one month and reinforcement. The participants of the program at a Japanese worksite replied for a one-year followed up survey. Forty-seven poor sleepers whose sleep onset latency was 30 min or more and/or sleep efficiency was less than 85% were analyzed. Eight sleep parameters and nine sleep-related behaviors were evaluated using questionnaires at baseline, post-intervention and follow-up. At one year, total sleep time increased by 27 min, sleep onset latency shortened by 17.5 min and sleep efficiency improved by 6.9 points. Desirable changes were obtained in 4 sleep-related behavior including not being active before bedtime, not working or watching TV in the bedroom, not oversleeping on holidays and having a relaxed bath time. These results suggest that this brief behavioral intervention could improve sleep quality through the modification of sleep-related behavior.