Introduction Sickness absence is a major public health problem. Research on sickness absence focuses on interventions aimed at expediting return to work. However, we need to know more about sustaining employees at work after return to work. Therefore, this study investigated the recurrence of sickness absence according to diagnosis. Methods We analyzed the registered sickness absence data of 137,172 employees working for the Dutch Post and Telecom. Episodes of sickness absence were medically certified, according to the ICD-10 classification of diseases, by an occupational physician. The incidence density (ID) and recurrence density (RD) of medically certified absences were calculated per 1,000 person-years in each ICD-10 category. Results Sickness absence due to musculoskeletal disorders had the highest recurrence (RD = 118.7 per 1,000 person-years), followed by recurrence of sickness absence due to mental disorders (RD = 80.4 per 1,000 person-years). The median time to recurrent sickness absence due to musculoskeletal disorders was 409 days after the index episode. Recurrences of sickness absence due to musculoskeletal disorders accounted for 37% of the total number of recurrent sickness absence days. For recurrences of sickness absence due to mental disorders this was 328 days and 21%, respectively. Unskilled employees with a short duration (<5 years) of employment had a higher risk of recurrent sickness absence. Conclusions Interventions to expedite return to work of employees sick-listed due to musculoskeletal or mental disorders should also aim at reducing recurrence of sickness absence in order to sustain employees at work.