Inspissated, sticky, immobile meconium causes this transient form of distal colonic or rectal obstruction in newborns. The incidence has been estimated at 1 in 500 to 1000 live births. The condition is thought to result from dehydration of the meconium. Meconium plug syndrome is associated with prematurity, toxemia of pregnancy, maternal use of phenothiazines or tricyclic antidepressants, hypotonia, hypermagnesemia, hypothyroidism, and sepsis. Most affected infants are otherwise healthy. Approximately 15% have cystic fibrosis, small left colon syndrome, or Hirschsprung disease. Clinical manifestations include significant abdominal distention and failure to pass meconium. Plain abdominal radiographs demonstrate multiple loops of distended bowel, often with air-fluid levels. The results of a barium enema reveal an enlarged rectum with meconium in the colon. Following the enema, large pieces of inspissated meconium plugs are usually passed and the obstruction is completely relieved. If the obstruction recurs, cystic fibrosis and Hirschsprung disease must be considered in the differential diagnosis.