Three of four siblings had sacral meningocele with subsequent development of hydrocephaly; two died during the neonatal period due to conotruncal heart defects (transposition of the great vessels and truncus arteriosus type I, respectively). An in utero diagnosis of open neural tube defect was made on the third sibling; persistent slightly elevated alpha-fetoprotein levels in amniotic fluid and increased number of rapidly adhering cells in short term amniotic cell culture were found. The unique combination of sacral meningocele and conotruncal malformations in this sibship suggests a new autosomal recessive condition. It also emphasizes the heterogeneity of both the open neural tube defects and congenital heart defects. Awareness of this variant is necessary in regard to the 25% recurrence risk instead of the 3% to 5% recurrence risk given for both congenital heart defects and open neural tube defects as isolated anomalies. The difficult prenatal diagnosis for the small neural tube defect should be appreciated.