A patient with Philadelphia (Ph1) chromosome-negative chronic granulocytic leukemia (CGL) had meningeal involvement three months after diagnosis. Leukemic blast cells had been noted in pleural fluid three weeks earlier. Her bone marrow remained in the benign phase. Three months of intensive therapy were required to clear the CSF of malignant cells. Myeloblastic transformation of bone marrow occurred 25 months after diagnosis, and attempts at induction of remission were unsuccessful. The CSF cytologic findings again were positive for leukemic cells the day before death, 29 months after diagnosis. Leukemic cells were found infiltrating the meninges at autopsy. This case illustrates that meningeal involvement may occur during the benign phase of Ph1 chromosome-negative CGL. Most previously reported cases of meningeal involvement by CGL have involved patients possessing the Ph1 chromosome, and in most cases meningeal involvement has followed malignant transformation of the bone marrow.