Following early autumn germination in Mojave Desert winter annual populations (53 taxa) sampled on 13 plots (total sample size, 16.4 m2) in three drainage basins in southern Nevada, 1963—64, there was 38% survival to maturity (plot range 10—63%). Death occurred in early spring, at the time of shift from the slow vegetative growth of winter to the beginning of stem elongation. Despite no marked precipitation deficiencies during the 7— to 8—month growing season, mortality apparently resulted from inadequate soil moisture to meet the demands of seedlings at the point in the life cycle of a manyfold increase in plant volume. Mean percentage survival to maturity of seedlings (58 taxa), sampled on 62 plots (total sample size, 62 m2) in sevean drainage basins, following spring germination after rains of 3—5.5 inches in March—April 1965, was 60% (range by basin, 44—83%). Mortality in these populations, whose life cycles were completed in 6—10 weeks, could not be attributed to inadequate moisture levels. In most seasons, regardless of precipitation regimes, the majority of seedlings of desert annuals probably do not survive to maturity.