Multifactorial sex-modified inheritance has been proposed as the model of transmission in familial Hirschsprung's disease (HD). A review of two separate kindreds suggests that aganglionosis may be inherited as an X-linked recessive or an autosomal dominant trait. Chromosomal anomalies and other syndromes, including G6PD deficiency, may occur with familial HD. Recurrence risk counseling for family members depends on accurate pedigree analysis and a comprehensive understanding of the genetic factors involved.