The paper is concerned with a single period problem when the demand is a stationary process, and the number of customers and order quantity are sufficiently large. Two estimators of the mean and standard deviation of the demand for unobserved lost sales are considered. The procedures are based on two censored samples: the observed selling durations, i.e. the moments of the last client’s arrivals during the stockout periods, and the demands. Marginal asymptotic distributions are used. The results of simulation for compound Poisson demand are given.