Background The introduction of part-time sick leave to enhance work participation has been adopted in several countries, including all Nordic countries.

Objectives To assess the effectiveness of the use of part-time sick leave at the early stage (first 12 weeks) of work disability due to mental disorder or musculoskeletal disease on work participation.

Method In a nation-wide register-based quasi-experimental study we compared sustained return to work (RTW) and 2 year work participation between the part-time and full-time sickness absence benefit groups using propensity score matching. Persons who received partial or full sickness absence benefit between January 1, 2010 and December 31, 2011 were eligible as cases or controls, respectively. Work participation was calculated as the proportion of time within 2 years when participants were gainfully employed and did not receive either partial or full ill-health-related or unemployment benefits.

Results Sustained RTW was observed more frequently in the part-time than in the full-time sick leave group. A difference was seen in both genders, those aged 45–64 years and especially in mental disorders. Overall work participation during the 2 year follow-up was at a higher level in the part-time sick leave group compared with the full-time sick leave group. The difference was larger in men than women and in mental disorders than in musculoskeletal diseases.

Conclusion The use of part-time sick leave during the first 12 weeks of work disability enhances overall work participation during a two-year period. The prescription of part-time sick leave can be recommended at an early stage of work disability.