Three cases of peritonial pseudocysts are reported with guidelines for the diagnosis of this type of complication. The authors point out the value of the following signs: 1 - increase of ventricular pressure with worsenning of the clinical picture; 2 - localized pain in the abdomen; 3 - difficulty to depress the capsule; 4 - occurrence of subcutaneous collection of CSF around the pathway of the catheter. In some occasions it is possible to palpate the mass of the pseudocyst. The presence of subcutaneous collection of CSF around the pathway of t!ie catheter is an important warning sign of peritonial pseudocyst and must be differentiated from that originated by the disconnection between the capsule and the catheter. In this condition however, the accumulation of liquid begins in the cervical region. Also in this case the capsule depresses easily. The most precise diagnosis is achieved by X-Ray. The authors describe a method that consists in introducing a needle through the capsule and injecting 8cc of Dimer-X contrast. The catheter and the cavity of pseudo-cyst appear contrasted in the X-Ray film, stablishing the definitive diagnosis. The authors discuss the physiopathogeny of CSF accumulation; once the pseudocyst is formed, the intracranial pressure increases, and the fontanelle bulges, this leads to repeated pumping by the relatives and subsequent rising of pressure within the pseudo-cyst. At this point the patient refers pain at the location of the pseudo-cyst and the CSF tends to leak around catheter. In babies the abdominal pain leads to crying, thus increasing once more the intra-cystic pressure which favors the leakage of CSF from the pseudo-cyst around the catheter.