Recent studies have suggested that portable monitoring may be a valid means of finding respiratory disturbances in epidemiologic research on a large scale. The aim of this cross-sectional study was to evaluate by means of an appropriately validated portable instrument (MESAM 4) the nocturnal oxygen desaturations in a representative sample of adult male population in North Italy. We randomly chose 750 subjects: 399 subjects (53.2 percent) agreed to participate and a complete evaluation of nocturnal recording was possible in 349 subjects (87.5 percent). Seventeen percent of subjects were every-night snorers; a number of oxygen desaturations per hour (ODI) > 10 was found in 13.7 percent, and an ODI > 20 resulted in 4.8 percent. Age, neck circumference corrected for height, snoring time (measured by MESAM), and self-reported snoring were the variables best explaining ODI in our multivariate approach. This study reports the highest prevalence, using nocturnal oxygen desaturation indices as marker, of sleep-disordered breathing than any reported until now in a general population.