Aims/hypothesis. Obesity is a complex trait influenced by multiple genes. We evaluated linkage in three regions of human chromosome 10 previously linked to obesity-related phenotypes. Methods. We conducted non-parametric linkage analysis of obesity-related phenotypes in cohorts of 170 European-American and 43 African-American families having extremely obese and normal weight subjects. Results. We found support for linkage of an obesity phenotype (BMI ≥ 27 kg/m²) in both cohorts, as well as in a combined analysis (European-American cohort, Z = 1.90, p = 0.03; African-American cohort, Z = 2.25, p = 0.014; combined cohort, Z = 2.55, p = 0.005). Conclusion/interpretation. These results confirm previous reports of linkage in French and German families. The consistency of results across these four cohorts supports the localization of a quantitative trait locus influencing obesity to human chromosome region 10p12. [Diabetologia (2001) 44: 363–366]