Paget's disease of bone is a common disorder characterized by focal abnormalities of bone turnover which are associated with bone pain bone deformity and an increased risk of pathological fracture. Genetic factors play an important role in the pathogenesis of Paget's disease, and recent genetic linkage studies have shown that in some families the disease is linked to a candidate locus on chromosome 18q21-22, which also harbors the gene for the related inherited condition, familial expansile osteolysis. In this study we characterized the patterns of inheritance in a series of 269 individuals from a further 50 kindreds with familial Paget's disease and sought to determine how frequently the disease was linked to chromosome 18q. Segregation analysis showed that 54% of individuals had developed Paget's disease by the age of 55, with an equal distribution in men in women, consistent with an autosomal dominant mode of inheritance with high penetrance. In families where parental data were available, there was no difference in the frequency of disease transmission between paternal or maternal sources. Linkage studies with nine polymorphic markers spread across the candidate region did not support linkage to 18q under models of homogeneity or heterogeneity. Indeed, the summated multipoint lodscores were consistently below -2.0 across the region, providing strong evidence against linkage. These studies confirm the presence of genetic heterogeneity in familial Paget's disease but show that linkage of the disease to the previously identified candidate locus on chromosome 18q21-22 is relatively uncommon.