1. Patients with disorders of entrainment to external time cues such as delayed sleep phase syndrome (DSPS) and non-24-hour sleep-wake syndrome (HNS) were treated with non-pharmacological interventions and/or pharmacological agents. 2. Resetting the circadian clock with chronotherapy was easy in all DSPS patients, but it was not as easy to maintain the reset rhythm without additional therapy. Triazolam was effective in treating the phase delay that reappeared after chronotherapy. 3. Vitamin B12 (methylcobalamin) was strikingly effective in some patients with DSPS or HNS. 4. All the adolescent patients who complained of inability to attend school finally returned to their classes after treatment. Maintaining the reset rhythm in adolescent patients was easier than in adults.