A family is reported in which the mother and 3 of her 5 children have a history of hypertrophic pyloric stenosis. The inheritance and roentgenographic signs of hypertrophic pyloric stenosis are discussed.The more recent genetic studies support the theory that hypertrophic pyloric stenosis is inherited as a dominant polygenic trait and that the threshold level for expression of the disease state is lower for males than for females. However, females that have hypertrophic pyloric stenosis carry a greater number of genes for the condition than a comparable male and have a greater risk of producing affected children.