The case of a 3-year old boy affected by acute leukemia and presenting a picture of meningeal involvement is discussed. The neurological ma- nifestations occurred after a period of 18 months of clinical and hematological remission. The symptoms were those of intracranial hypertension; presence of numerous leukemic cells in the cerebrospinal fluid and widening of cranial sutures were observed. A two months course of treatment with intrathecal injection of 5 mg Amethopterin each brought about an excellent neurological recovery that is lasting for more than 4 months. The injections were made firstly at a five day interval, which was increased at the end of the treatment. The experience of this case added to those of prior cases documented in the literature stresses the importance of the problem. It is suggested that every case of leukemia be thoroughly examined and if symptoms and signs of neurological involvement were found, cerebrospinal fluid examination must be performed. Thus acting it will be possible to diagnose nervous system involvement and start the treatment at earlier stages. In this way the patient may have a better and longer life. The graph clearly shows the importance of cerebrospinal fluid examinations to evaluate the results of the treatment.