We present the program spip for simulating multilocus genetic data on individuals in age-structured populations. In addition to genetic data on sampled individuals, the pedigree connecting all individuals in the population is recorded. This allows investigation of the relationship between family structure and population parameters. We foresee that spip will be useful for evaluating multilocus estimators of pairwise relatedness and population structure, and for simulating the distribution of relatedness in populations with varying demographies. It also provides a method for simulating genetic drift in complex populations.