Churg-Strauss syndrome (CSS) and Wegener's granulomatosis (WG) are uncommon primary vasculitides, characterized by the involvement of the small to medium size vessels and by the frequent presence of serum antineutrophil cytoplasmic antibodies (ANCA). The pathogenesis of ANCA associated vasculitides is unclear, but roles for both genetic and environmental factors have been suggested. Familial cases of WG, but not CSS, have been reported. We describe the occurrence of CSS in a man and, 5 years later, WG in his son. These patients live together in an urban area of Northern Italy and share the HLA haplotype A*03; B*07; C*w07; DRB 1*0404, DQB 1*0302. To our knowledge, this is the first report of the familial clustering of CSS and WG in first-degree relatives.