Previous studies have reported a great difference in snoring prevalence in different populations. In a recent study on men and women 20-45 y old, living in Sweden (Uppsala, Gothenbourg), Iceland (Reykjavík) and Belgium (Antwerp), data concerning snoring, etc., were collected using the same questions and scales in all the countries. In all four areas the prevalence of snoring was the same: 5% of men and 2-3% of women reported snoring every night. In all areas snoring was positively correlated with age, male sex and body mass index. It was therefore assumed that the previous difference in snoring prevalence is probably an artifact of different methodologies. The connection between snoring and systemic hypertension has been much disputed during the last decade. The high prevalence of hypertension in the sleep apnoea syndrome has been explained by obesity/age/male gender/sleep apnoea and/or snoring. In one recent study snoring did not contribute independently to the prediction of hypertension, while other studies indicate that snoring is an independent risk factor for hypertension. After reviewing some of the epidemiological literature it was found that these studies are bound to identify almost entirely different subgroups of the population as snorers since the prevalence of snoring is rated on different types of frequency scales with words like 'never', 'often' or the number of nights per week. The questions used are also different. In general it can be stated that the smaller the proportion of the population identified as snorers the more often there is a statistically significant association with hypertension. The relationship between snoring and hypertension is considered to be unclear due to the different research methods used, and to the uncertain role played by confounding factors such as obesity. There is a need for population-based, prospective, studies with more uniform definitions of the term 'snoring' based on objective measurements of upper airway resistance during sleep, together with haemodynamic studies.