Many long-lived plant and animal species have nondiscrete overlapping generations. Although numerous models have been developed to predict the effective sizes (N(e)) of populations with overlapping generations, they are extremely difficult to apply to natural populations because of the large array of unknown and elusive life-table parameters involved. Unfortunately, little work has been done to estimate the N(e) of populations with overlapping generations from marker data, in sharp contrast to the situation of populations with discrete generations for which quite a few estimators are available. In this study, we propose an estimator (EPA, estimator by parentage assignments) of the current N(e) of populations with overlapping generations, using the sex, age, and multilocus genotype information of a single sample of individuals taken at random from the population. Simulations show that EPA provides unbiased and accurate estimates of N(e) under realistic sampling and genotyping effort. Additionally, it yields estimates of other interesting parameters such as generation interval, the variances and covariances of lifetime family size, effective number of breeders of each age class, and life-table variables. Data from wild populations of baboons and hihi (stitchbird) were analyzed by EPA to demonstrate the use of the estimator in practical sampling and genotyping situations.