Background: Previous research indicates that long working hours, time pressure and overtime work relate to a range of adverse outcomes including poor recovery and health complaints. But, findings are inconclusive and limited, especially regarding the associations to sick leave. The aim was to study if time pressure or sleep problems due to thoughts about work were associated with future sick leave, when adjusting for confounders including familial factors, and stratifying by occupational sector. Methods: The study sample included 23,777 twin individuals (54.5% women), aged 19-47 years who participated in a survey in 2005 including questions on time pressure, sleep, work and health. Register data on sick-leave spells lasting >14 days were obtained from the National Social Insurance Agency. Individuals were followed from date of survey response until 12/31/2013. Associations between time pressure, sleep problems due to thoughts about work and future sick leave were investigated using logistic regression analyses to assess Odds Ratios (OR) with 95% Confidence Intervals (CI). Results: Thirty-five percent of the individuals had an incident sick leave spell during the 8-years of follow-up. Sleep problems due to thoughts about work once a month or more often were associated with sick leave in the fully adjusted model (OR 1.22, CI 1.10-1.36). Stratified by sector, the highest estimate was shown for state employees (OR 1.54, CI 1.11-2.13). Familial factors did not seem to influence the associations. We found no statistically significant associations between time pressure and sick leave. No sex differences were found. Conclusions: Results indicate that sleep problems due to thoughts about work is a risk factor for future sick leave. This follows previous research showing that sleep length and disturbances, regardless of their reasons, are associated with sick leave. But, experiences of work-related time pressure seem not to be associated with sick leave.