Infantile cortical hyperostosis is a rare proliferative bone disease affecting infants under the age of 6 months. In 1961 a large family of French-Canadian origin in which 14 children in three generations were affected was described. Since then 20 new cases have been found in this family. This is the largest familial aggregation of this disease reported in the literature to date. On the basis of the findings in this pedigree, the familial form of the disease appears to be transmitted by a single autosomal dominant gene with incomplete penetrance and variable expressivity.