The phenomenon of genomic imprinting describes the differential behavior of genes depending on their parental origin, and has been demonstrated in a few rare genetic disorders. In complex diseases, parent-of-origin effects have not been systematically studied, although there may be heuristic value in such an approach. Data from a genome scan performed using 356 affected sibling pair families with type 1 diabetes were examined looking for evidence of excess sharing of either maternal or paternal alleles. At the insulin gene (IDDM2), evidence for excess sharing of alleles transmitted from mothers was detected, which is consistent with transmission disequilibrium results published elsewhere. We also identified additional loci that demonstrate allele sharing predominantly from one parent: IDDM8 shows a paternal origin effect, IDDM10 shows a maternal effect, and a locus on chromosome 16q demonstrates a paternal effect. We have also evaluated these loci for confounding by differences in sex-specific meiotic recombination by performing linkage analysis using sex-specific genetic maps. The analysis of the parental origin of shared alleles from genome scans of complex disorders may provide additional evidence for linkage for known loci, help identify regions containing additional susceptibility loci, and assist the cloning of the genes involved.