A case is described where phototherapy rapidly restored sleep-wake disturbances and concurrent symptoms of delirium in a patient who did not respond to conventional treatment with haloperidol. In this case, the delirious state may have been caused by a change in metabolism as a result of sepsis. Exposition of the patient to 8,000 Lux during 1.5 h for 5 consecutive days was sufficient to suppress all delirious symptoms and to normalize sleep. This result may encourage the setup of systematic studies towards the extent of desynchronization between various rhythmic cycles in delirium and towards the value of phototherapy for the restoration of normal circadian rhythmicity.