Review of 27 cases of massive ascites found in the first month of life, usually immediately after delivery, revealed a broad spectrum of causes. Seven newborns had urinary ascites, five had bowel disease, three had cardiac arrhythmias, two had liver disease, and one each had toxoplasmosis, ovarian cyst, and chylous ascites. In seven cases the cause was never established. Physical examination, a planned sequence of radiologic examinations, and paracentesis for fluid analysis when necessary are the major steps in differential diagnosis. A systematic approach to the problem is proposed.