Background: Cerebrospinal fluid (CSF) opening pressure (OP) of >= 28 cm H2O is now considered a diagnostic criterion for Pseudotumor cerebri syndrome (PTCS) in children. However, it has been proposed that a diagnosis of "probable" PTCS can be made with an OP30 cm H2O in seven children. MRI findings supportive of PTCS were seen in eight patients. Conclusions: The diagnosis of probable PTCS as a subgroup of PTCS can be convincingly made in children with an OP < 28 cm H2O. Results of opening pressure measurement always need to be interpreted within the whole clinical context. Treatment decisions in patients with "probable" PTCS should follow the same stage-based principles as for "proven" PTCS. (C) 2016 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.