The first paper of this issue of Sleep and Breathing reports that the quality of life (QOL) assessed by the SF-36 and the Epworth Sleepiness Scale (ESS) in obesity hypoventilation syndrome (OHS) was compared with age- and body mass index-matched patients without hypoventilation (obese OSA), nonobese OSA patients, and healthy subjects. The QOL in OHS was worst among these four groups. After 3 to 6 months of nasal continuous positive airway pressure (CPAP) treatment, the QOL in OHS improved to the normal level similar to the two other OSA groups. We have observed severe nonobese OSA patients with hypoventilation. One of the risk factors, which related to a severe general condition, seems to be a small craniomandibular structure, which could induce an increase in upper airway resistance during sleep. Characteristics of Japanese OSA patients may be different from those in other countries. Although belatedly, the clinical study and management of sleep disordered breathing have just begun.