In the absence of the price mechanism, hospital emergency departments relyon waiting times, alongside prioritisation mechanisms, to restrain demand andclear the market. This paper estimates by how much the number of treatmentsdemanded is reduced by a higher waiting time. I use variation in waiting timesfor low-urgency patients caused by rare and resource-intensive high-urgencypatients to estimate the relationship. I find that when waiting times are higher,more low-urgency patients are deterred from treatment and leave the hospitalduring the waiting period without being treated. The waiting time elasticity ofdemand for low-urgency patients is approximately -0.25 and is highest for thelowest-urgency patients