Objective:This study evaluated utilization of mental health and substance use services among enrollees at a large employee health plan following changes to benefit limits after passage in 2008 of federal mental health parity legislation.Methods:This study used a pre-post design. Benefits and claims data for 43,855 enrollees in the health plan in 2009 and 2010 were analyzed for utilization and costs after removal of a 30-visit cap on the number of covered mental health visits.Results:There was a large increase in the proportion of health plan enrollees with more than 30 outpatient visits after the cap's removal, an increase of 255% among subscribers and 176% among dependents (p<.001). The number of people near the 30-visit limit for substance use disorders was too few to observe an effect.Conclusions:Federal mental health parity legislation is likely to increase utilization of mental health services by individuals who had previously met their benefit limit.