Sickness funds information has given conflicting evidence on the evolution of morbidity during the mortality decline. Evidence on increased morbidity has been explained by an actual increase of morbidity, a cultural inflation of morbidity or changing institutional settings, however, morbidity rates have also been shown to be stable over time when age composition of members is controlled for. Most previous studies have been confined to data on men; however, in an earlier article, Castenbrandt found large gender differences in historical sick leave by using national statistics on both men and women. To move forward, this article aims to analyse trends in sickness claims during the mortality decline in the early twentieth century using individual level data from Swedish sickness funds covering the period 1898–1950. Concretely, we investigate gender differences in sickness claims (incidence and duration) and how institutional settings (member composition and fund-specific regulations) affected the sick leave patterns.