The aim of the present study was to explore morbidity and healthcare utilisation among young adult males with obstructive sleep apnoea (OSA) compared with middle-aged OSA patients over the 5-yr period preceding diagnosis. A prospective case-control study was performed; 117 young (22-39-yr-old) males with OSA were matched with 117 middle-aged (40-64-yr-old) OSA males for body mass index, apnoea/hypopnoea index, arterial oxygen saturation, arousal and awakening index, and Epworth Sleepiness Scale score. Each OSA patient was matched with controls by age, geographic area and physician. Young adult males with OSA showed no increase in specific comorbidity compared with controls. Middle-aged OSA patients exhibited increased risk of cardiovascular disease. Healthcare utilisation for the 5-yr period was >or=1.9 times higher among young and middle-aged male OSA patients than among controls. Multiple logistic regression analysis revealed that hyperlipidaemia in young adults and a body mass index of >37 kg x m(-2) and cardiovascular disease in middle-aged adults are the only independent determinants of the upper third, most costly, OSA patients. Compared with middle-aged males with obstructive sleep apnoea, in whom increased expenditure was related to cardiovascular disease and body mass index, utilisation was not related to any specific disease in younger cases.