A system of 15 socio-economic groups (SOEG) based on occupation and position within occupation is proposed and discussed as a basis for statistical analyses of mortality data. In order to check the validity of this classification, a random sample of 3058 male death certificates is compared with the information obtained from the corresponding 1980 census records. The comparison reveals that most of the SOEGs have satisfactory validity. The same is true for a model emulating the widely used English system of Social Classes (SC). Estimates of the differences in mortality between SOEGs or SCs can be improved significantly applying correction factors derived from the sample of linked death certificates and census records.