This study examines the association of Hirschsprung disease with Down syndrome and calculates the recurrence risk for families of Hirschsprung patients. Information was collected from 134 histologically diagnosed patients with Hirschsprung disease, from Children's Hospital in Pittsburgh, PA between 1950 and 1977. One hundred and three patients had short segment Hirschsprung disease which is defined as involvement up to and including the sigmoid colon. Thirty-one patients had the long segment type with aganglionosis extending in some cases to the small intestine. As in other studies, we found a significant association between Hirschsprung disease and Down syndrome in that 5.9% of probands had both. Mean maternal age of cases with both Hirschsprung disease and Down syndrome (33.5 years) was significantly different from controls (26.7 years) and non-Down syndrome Hirschsprung patients (26.6 years). The overall sex ratio for Hirschsprung disease was 3.6. Recurrence risks were dependent on proband sex and the degree of aganglionic involvement.