Genetic polymorphism of orosomucoid (ORM1) was studied by isoelectric focusing in 3,817 conscripts and blood donors from the counties of Norrbotten and Västerbotten in northern Sweden. The individuals were distributed according to place of birth into 23 subpopulations. There was a significant heterogeneity between the 23 subpopulations with respect to the allele frequencies (p = 1.10–8). The ORM1*2 allele varied between 27 and 46%, and a clineal variation was observed with decreasing ORM1*2 allele frequencies in the northern direction. Significant correlations were found between the frequencies of the ORM1 alleles and previously studied Finnish and Saamish marker genes. The geographical variation of ORM1 alleles was in close agreement with the pattern expected from the known mixture of Finns, Saamis, and Swedes in northern Sweden and further underlines the impact of ethnic heterogeneity on the genetic differentiation of the north Swedish populati