We assess how cost sharing for medical services affects restricted activity days (RADs) and work loss disability days (WLDs), using data from a controlled experiment. We grouped the experimental insurance plans into four categories, one providing free care and the other three requiring varying amounts of cost sharing. RADs per person per year decreased by one to two days with greater cost sharing, with the strongest effects among those of average or poor health status, especially the non-poor. Unlike RADs, WLDs showed no systematic differences by plan.