Six premature infants (birth weights 920-1320 g) developed marked abdominal distension after birth, and contrast enema examination showed a microcolon. Four of the six were born to mothers with toxemia who received magnesium sulfate. Bilious emesis was absent in all six, despite marked distension and failure to pass meconium. None of the patients had aganglionosis or cystic fibrosis; five of six were followed without surgery and recovered spontaneously. The sixth had perforation 8 hr after contrast enema and required bowel diversion; this infant also survived. This appears to be an equivalent form in small premature infants of the "small-left-colon syndrome" seen in term infants. Surgery should be reserved for complications; it is not necessarily indicated by the finding of a microcolon in such patients.