A 7-y-old boy with acute lymphoblastic leukaemia (ALL) received 600 mg of i.v. methotrexate (MTX) over 2 h, followed by triple intrathecal therapy (TIT) with cytosine arabinoside 30 mg, methylprednisolone 10 mg and MTX 300 mg (instead of the prescribed 12 mg). Ninety minutes later the patient developed headache, loss of consciousness and generalized hypertonia. He was transferred to the Intensive Care Unit, intubated and treated with phenobarbital. Three hours after the TIT, the levogyrus form of folinic acid (equivalent to double doses of the racemic product) was started i.v. at a dose of 100 mg every 3 h for 24 h, and every 6 h in the following 24 h. Cerebrospinal fluid was examined and was found normal. The patient subsequently remained in normal neurological status. The favourable outcome in our case suggests that folinic acid rescue may be adequate to prevent sequelae in patients who undergo intrathecal MTX overdoses up to 300 mg.