An evaluation of patients with meconium peritonitis shows that, apart from the fibro-adhesive type, the (Pseudo) cystic and the generalized type, a fourth type can be distinguished. In a case of this fourth type, the "microscopic" type of meconium peritonitis, no signs of a peritonitis are found on macroscopic examination of the abdominal cavity. Conversely, microscopic examination will reveal meconium components focally outside the bowel. The clinical and histological data of 14 patients are discussed. It is pointed out that a significantly large number of patients with meconium peritonitis also have atresia of the small bowel. Based on the patient evaluation, a hypothesis is brought forward concerning the pathogenesis of these atresias.