The objective was to compare the applicability of and results provided by the two measures of sickness absence used most often within the Swedish social insurance administration (that is, unadjusted sick-leave rate and adjusted sick-leave rate) and five measures suggested by epidemiological researchers. Data consisted of four cross-sectional data sets of registry sick-leave data covering four separate years (1997-2000) in three counties. In total 454,000 persons qualified for sickness insurance and aged 20-64 years were included. The two measures used within the social insurance administration and three of the five measures suggested by epidemiological researchers revealed sex-related dissimilarities in absence patterns that indicated that women had more sickness absence than men. However, in marked contrast to those results, two of the epidemiologically based measures (i.e., length of sickness absence and duration of sickness absence) instead showed highly comparable rates of sick leave for men and women, and such information is seldom obtained, albeit definitely of importance, when trying to make a correct assessment of sickness absence. The measure of sickness absence that is used influences the findings and should therefore be chosen with care. Complementing the measures used in the social insurance administration by five measures suggested by epidemiological researchers provided a more informative and comprehensive picture of sickness absence in a population. Further investigations into the effect of using different measures is needed, as well as international consensus on what to call different measures.