Seven full-term infants with aganglionosis extending into the small bowel presented with clinical, radiological, and operative features of meconium ileus. Misdiagnosis resulted in inappropriate treatment. The correct diagnosis was eventually established by rectal suction biopsy, mostly after either recurrent intestinal obstruction or stomal dysfunction, and after cystic fibrosis had been excluded. For two patients, the results of rectal suction biopsies were initially misleading. Two infants died. Extensive intestinal aganglionosis should be considered a rare possibility in all infants with meconium ileus. In such cases, histological examination of the appendix may avoid this potential pitfall.