This study examined whether worktime control buffered the impact of worktime demands on work-family interference (WFI), using data from 2,377 workers from various sectors of industry in The Netherlands. We distinguished among three types of worktime demands: time spent on work according to one's contract (contractual hours), the number of hours spent on overtime work (overtime hours), and the number of hours spent on commuting (commuting hours). Regarding worktime control, a distinction was made between having control over days off and (...) vacations (leave control) and having control over starting and finishing times (flextime). These three worktime demands were expected to have separate as well as joint effects on WFI, whereas worktime control should buffer these adverse effects of worktime demands on WFI. Stepwise regression analyses showed that working high numbers of contractual and overtime hours was indeed associated with high WFI. Further, worktime control indeed made a difference in terms of WFI: whereas leave control contributed directly to lower WFI, flextime buffered the adverse effects of long contractual workhours. Our results suggest that very long working days should be prevented, and that worktime control may be a powerful tool to help workers maintaining a good work-family balance. (shrink)