Paget's disease of bone is a common condition characterized by bone pain, deformity, pathological fracture, and an increased incidence of osteosarcoma. Genetic factors play a role in the pathogenesis of Paget's disease but the molecular basis of the disease remains unclear. Previous genetic linkage studies have mapped the rare Paget's disease‐like bone dysplasia familial expansile osteolysis (FEO) to chromosome 18q21–22, and recent work has shown evidence of linkage between this locus and Paget's disease in one family. Here we studied the relationship between the 18q21–22 locus and Paget's disease in eight large multiplex families from diverse ethnic backgrounds with inherited Paget's disease. Paget's disease was inherited as an autosomal dominant trait in all families, with high penetrance by the sixth decade. Analysis of seven highly polymorphic markers from chromosome 18q21–22 showed positive summated two‐point log₁₀ odds ratio (lodscores) of +2.97 with the marker D18S42 at a recombination fraction (θ) = 0.05, and of +2.95 with the marker D18S60 at θ = 0.00, values which are close to the cut‐off of +3.0, which is generally accepted as evidence of linkage. Segregation analysis of the haplotypes and formal statistical analysis using the HOMOG program provided evidence for genetic heterogeneity, however, with evidence for linkage in five families and against linkage in the remaining three families (chi square 8.82; df = 2; p < 0.025). Multipoint linkage analysis in the five linked families showed lodscores of above +3.5 across the whole susceptibility region and a maximum summated lodscore of 3.89 at the marker D18S465. In the three nonlinked families, negative multipoint results were obtained for the whole region, with lodscores below –2.0 in one family, excluding this as a candidate locus for the disease. Our studies demonstrate the importance of hereditary factors in the pathogenesis of Paget's disease and confirm evidence of linkage between Paget's disease and chromosome 18q21–22 in some families. This raises the possibility that Paget's disease and FEO may share a common molecular basis, perhaps due to different mutations in the same gene or family of genes. Data from three families did not support evidence of linkage to 18q21–22 however, indicating that Paget's disease is genetically heterogeneous and suggests the presence of at least one additional locus which remains to be discovered.