Thirty-five spinal fluids with leucocytosis belonging to 26 children presenting neoplasia without metastases or CNS infection, were studied. We found that 69% of the cases were receiving some kind of CNS therapy, although leucocytosis could be found at any moment of the evolution and independently of treatment. It is stressed that the criteria for meningeal infiltration in children with neoplasia must be established only if tumoral cells are found in the spinal fluid. Pleocytosis and absence of symptomatology must not be used as the main criteria.