Three children with subacute neonatal intestinal obstruction are described in whom the diagnosis of congenital megacolon was suspected. The radiological changes improved when oral feeding stopped but reappeared when it was restarted. The aetiology remained unrecognised until the results of the neonatal screening for hypothyroidism showed all three cases had congenital hypothyroidism. The severity of the disorders was unusual and remains unexplained. Systemic TSH and/or T4 determinations should lead to a better understanding of the disorders due to hyperthyroidism in neonates.