Delayed sleep phase syndrome (DSPS) is a common but little reported cause of severe insomnia. Affected individuals complain of difficulty falling asleep and difficulty awaking at socially acceptable hours. It results from a dysregulation of the circadian sleep-wake cycle. DSPS presents in clinically heterogenous ways as modulated by motivation, psychopathology, drug status, and treatment compliance factors. Patients respond variably to the range of possible treatments. Bright light treatment potentially corrects the circadian abnormality of DSPS. Other treatments reported to relieve some DSPS patients include schedule shifts, drugs, and vitamin and hormone treatments. The safety and efficacy of light treatment have not been conventionally defined, but available information suggests that it is ophthalmologically safe. At present, DSPS must be managed empirically by various methods.