Analysis of 100 consecutive patients with pyloric outlet obstruction revealed that 37% of the obstructions were secondary to peptic ulcer disease and 42% were caused by malignant neoplasm. Only a single patient with primary hypertrophic pyloric stenosis was identified, and whether this lesion is a cause or effect of peptic ulcer disease remains unclear. Similarly, the association of this entity with congenital pyloric stenosis is unknown.