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A patient with obstructive sleep apnea was monitored five times during three years while his weight fluctuated within a range of 26 kg. The number of apneas per hour of sleep varied from 59.6 at 111 kg of weight to 3.1 at 85 kg. The relation between apneas per hour of sleep and body weight was a logarithmic function. A modest decrease in weight was thus associated with a disproportionally larger decrease in the rate of apneas. Typical SaO 2 levels during the apneic episodes also had a logarithmic relation with body weight. Apnea-related sinus bradycardia and sinus tachycardia were only present at the highest weight. The results suggested that dieting and weight loss lead to an improvement in sleep apnea and related sequelae.Obstructive sleep apnea syndrome is characterized by a repetitive and periodic occlusion of the upper airway during sleep. The mechanisms involved in this disorder are not well understood at present. 1 Obesity is seen in the majority of patients with sleep apnea. Redundant tissue in the oropharyngeal airway associated with obesity is thought to be a contributing factor. Surgical intervention by tracheostomy or uvulo-palato-pharyngoplasty is the treatment of choice, especially in the presence of apneic-induced cardiac arrhythmias, but case reports have suggested improvement in the obstructive sleep apnea and related sequelae following weight loss. 2-4 The exact relation between this syndrome and body weight remains ambiguous, however, as previous reports are based on single observations following weight reduction. We have monitored the sleep of a patient with obstructive sleep apnea five times during the course of nearly three years while his weight fluctuated from 85 kg to 111 kg. A logarithmic relation between the rate of apneas during sleep and body weight is demonstrated by this patient. Case ReportA 52-year-old white man was referred for evaluation of uncontrolled daytime sleepiness. The patient reported a 19-year history of hypersomnia and falling asleep at inappropriate times. Symptoms were reported as relatively stable over the past ten years. The patient noted loud snoring and excessive sweating during sleep. Although he denied cataplexy, hypnagogic hallucinations and sleep paralysis, narcolepsy was diagnosed two years prior to our evaluation based solely on the reported hypersomnia.Physical examination revealed an obese man (173 cm tall, weighing 111 kg), extremely drowsy, but otherwise in no distress. Pertinent medical disorders included essential systemic