Obesity is one of the factors which increase the risk of decompression sickness. It has been suggested that any diver whose weight is more than 20% in excess of that derived from currently accepted tables should therefore be stopped from diving until he has lost enough weight. Published tables of average and standard weights for men, however, are unsuitable for application to men recruited for commercial diving, as the populations on which the tables were based differ in important respects from divers. Furthermore, the tables may assume that men are weighed and measured clothed and in shoes, whereas in most medical examinations the measurements are made on men without shoes and partially clad . Analysis of weight measurements of 1520 divers whose records are in the Decompression Sickness Central Registry in Newcastle upon Tyne suggests that divers as a group are substantially heavier than other populations on whom height-weight tables have been based. A table derived from American data of 1935-53 is often used as a guide. If this table is used the percentage of divers rejected as overweight may be as high as 13.6%. More recent and more appropriate data on heights and weights are required for use as reference standards for divers, or perhaps another measurement indicating obesity should be used.