A case of a nine-year-old boy who presented with central nervous system leukemia is described. This case was unusual because he presented without initial bone marrow involvement. Bone marrow involvement was documented 15 months after central nervous disease was diagnosed. Immunologic marker studies revealed that the spinal fluid blasts lacked definable B-cell, pre-B cell, T-cell, and pre-T cell surface markers. The marker studies helped to define the nature of the disease process.