On the basis of accumulating evidence that obesity has a substantial genetic component, a genomewide search for linkages of DNA markers to percent body fat is ongoing in Pima Indians, a population with a very high prevalence of obesity. An initial screen of the genome (>600 markers in 874 individuals) has been completed using highly polymorphic markers (mean heterozygosity = .67). Reported here are the sib-pair linkage results for percent body fat (277 siblings), the best available indicator of overall obesity. Single- marker linkages to percent body fat were evaluated by sib-pair analysis for quantitative traits. From these analyses, the best evidence of genes influencing body fat came from markers at chromosome 11q21-q22 and 3p24.2- p22 (P = .001; LOD = 2.0). Regions flanking these markers were further investigated by multipoint linkage. The evidence for linkage at 11q21-q22 increased to P = .0002 (LOD = 2.8), peaking between markers D11S2000 and D11S2366. Evidence for linkage at 3p24.2-p22 did not change. No association was detected for any marker in the region. Although several genes are known in the 11q21-q22 region, none have been implicated as candidate genes for obesity.