Genetic affinities of 21 tribal populations of Andhra Pradesh are reported in terms of genetic distance analysis with regard to AB0 and Rh loci. These tribal populations show a high degree of differentiation in the distribution of AB0 blood groups. Some tribes exhibit the monomorphism for Rh (D) locus. The genetic distance analysis reveals that the 21 tribes included in this study are genetically distant from one another and the genetic clustering pattern correlates with linguistic/ethnic affiliation and geographical propinquity of these tribal populations to a certain extent. The possible reasons for different cluster formations are discussed.