Purpose: Delayed sleep-wake phase disorder is the most common circadian rhythm sleep disorder. The aim of this article is to describe the case of a man whose unhealthy lifestyle and improper treatment made delayed sleep-wake phase disorder turn into non-24-hour sleep-wake rhythm disorder.

Case description: A 26-year old patient reported to a sleep disorder outpatient clinic, complaining of an irregular sleep rhythm. He said that from the beginning of the primary school, he had problems with falling asleep and waking up in the morning to go to school. These difficulties got more severe during adolescence and after he started his college studies. The rhythm of sleep became irregular and the need to sleep increased to 13 hours a day. The treatment involved behavioural interventions combined with melatonin 5 mg/day and phototherapy, in line with the procedures of chronobiological treatment of sleep rhythm disorders.

Comment: Chronobiological interventions, such as monitoring of adherence to sleep hygiene rules with an emphasis on fixed, regular times of waking up (and falling asleep) both on weekdays and weekends, while limiting the use of multimedia devices emitting light, at least one hour before going to bed, play an important role in the treatment of delayed sleep-wake phase disorder. Failure to meet these rules makes the symptoms of the disorder more severe and in extreme cases can lead to total loss of synchronisation of the sleep and wake rhythm with the day and night rhythm.