This paper details genetic characterization and trends from a microsatellite-based study of genetic diversity on southern African pig populations. A total of 351 pigs from three commercial breeds and three indigenous populations were genotyped at 39 loci. Differences among the levels of genetic diversity in populations correlated well with known population histories. In commercial breeds, heterozygosity was higher in the well established SA Landrace and Large White breeds (0.580 and 0.636) compared to the Duroc breed, established more recently (0.531). In indigenous populations, the highest heterozygosity levels were found in the Mozambican and South African populations (0.692 and 0.634) with a lower value of 0.531 in a smaller Namibian population. A hierarchical division of total genetic diversity revealed a high between-population component of 17.9%. FST– and RST-based analysis confirmed high levels of differentiation, with pair-wise comparisons between breeds indicating significant differentiation in 20 out of 21 comparisons. Results from an assignment test confirmed results from FST and RST and suggested a true genetic structure with significant differentiation between most populations sampled, but with little differentiation among the commercial SA Landrace and Large White breeds. The results are discussed with reference to known historical information on commercial and indigenous pig populations. This paper also presents new data on the optimization of microsatellite markers for application in Sus scrofa domestica.