The leukemias and lymphomas represent a heterogenous group of hematologic malignancies with protean manifestations. Neurologic sequelae of the diseases have been recognized almost since the time the conditions were first described in the mid-1800s. Although our understanding of the various presentations of these blood disorders has evolved along with our knowledge of the malignancies, accurate diagnosis can still be difficult. It is critical for neurologists to have a high index of clinical suspicion to appropriately recognize the heralding features. This review focuses on the relevant clinical neurologic features and diagnostic studies to identify leukemias and lymphomas affecting the nervous system.