The estimation of P(Sn > u) by simulation, where Sn is the sum of independent, identically distributed random varibles Y1, . . . , Yn, is of importance inmany applications. We propose two simulation estimators based upon the identity P(Sn > u) = nP(Sn > u, Mn = Yn), where Mn = max(Y1, . . . , Yn). One estimator uses importance sampling (for Yn only), and the other uses conditional Monte Carlo c...