Mortality rates for males aged 20 to 64 in Scotland (1980-1982) display an increasing gradient both by social class (from class 1 to 5) and by the deprivation category of the area (from affluent to deprived) in which the event occurred. Social classes also exhibit gradients in mortality across deprivation categories, the corresponding rates in the most deprived category being around twice those in the most affluent areas. The gradients by deprivation category remain after standardizing for differences in social class composition. Within health boards in Scotland populations show only minor variability in terms of social class, while their composition on the dimension of deprivation is markedly diverse, and the classification of populations by the deprivation category of their area of residence appears to offer a superior basis for the explanation of differences in mortality between health boards than does social class. This evidence of area effects supports a proposal for area socioeconomic characteristics to be adopted as key variables in epidemiological analysis, and for an area classification to be designed and incorporated in the 1991 census output for use on a consistent basis.