Nationwide surveys from Finland, Norway and Sweden were analysed to examine socioeconomic inequalities in illness. This article first describes differentials in self-reported limiting long-standing illness and its distribution according to educational level. Age-standardized prevalence rates according to education are examined, and top and bottom prevalence ratios are compared between countries and genders. Secondly, the article attempts to assess the 'global' extent of inequalities in illness. This is made by calculating concentration indices for each country and gender. The description shows large illness differentials according to educational level in each country. A similar socio-economic pattern emerges from all three countries and both genders; i.e. lower socio-economic positions are associated with higher illness levels. This pattern is more distinct for men than for women. The gap in illness between top and bottom educational groups is widest for Norwegian men and smallest for Finnish women. However, top and bottom comparisons overlook other than the extreme groups, and give no information on the sizes of the groups. To avoid these problems concentration indices were calculated to assess the extent of inequalities in illness. According to these indices Norwegian men also show the highest extent of inequality, but differences to Swedish and Finnish men are small. The extent of inequality among women is smaller than among men; among Finnish and Norwegian women it is smaller than among their Swedish counterparts. Measures of inequalities such as the concentration index are useful tools, although complex inequalities cannot be captured by single measures. In the assessment of health inequalities not only relative but also absolute differentials need to be considered.(ABSTRACT TRUNCATED AT 250 WORDS)