The aim of this study is to evaluate if the long-term interventricular communication following aqueductoplasty is determined by the etiology of the aqueductal stenosis (AS).We retrospectively analyzed 27 patients who underwent endoscopic aqueductoplasty or endoscopic interventriculostomy with or without a stent for the treatment of AS or isolated fourth ventricle. Surgeries were performed between July 1997 and June 2003. Mean age at the time of surgery was 8 years. Mean follow-up is 24 months.We divided the patients into three groups. Group 1 consisted of 5 patients with membranous distal AS. Four patients were sufficiently treated by aqueductoplasty alone and 1 asymptomatic restenosis occurred. Group 2 consisted of 4 patients with AS due to a periaqueductal tumor. Three patients underwent aqueductoplasty and tumor biopsy with subsequent restenosis of the aqueduct. One patient underwent aqueductoplasty with a stent and tumor biopsy at the same time. Group 3 consisted of 18 patients with isolated fourth ventricle. The initial surgery was successful in 11 patients. Seven patients required revisions.The long-term communication following aqueductoplasty is determined by the etiology and morphology of the AS. In patients with a membranous distal AS aqueductoplasty alone will suffice. In patients with tumor-associated AS aqueductoplasty alone will not stay open. Those patients would better be treated with third ventriculostomy. In patients with isolated fourth ventricle the risk of restenosis is high. Therefore, we favor primary stent placement.