Measurements and simulations of the proton beam interaction with the mercury target were performed to support Spallation Neutron Source design. Due to the abundance of isotopes produced in mercury, the long delay between the irradiation and the measurements, and the self-shielding of the mercury sample, the measurements were difficult to perform and the activities of several isotopes have large uncertainties. Calculations predicted the activities of the most reliably measured isotopes within 20 %–40 %; however, some large discrepancies were observed for some isotopes for which the measurements were considered less reliable. Predicted dose rates were in very good agreement with the measurements.