Cancer involves a complex spectrum of disease conditions. However, cancer has received relatively limited attention in paleopathology and bioarchaeology as it is infrequently encountered in the skeletal record, and its differential diagnosis in dry bone remains challenging. Of all neoplastic disorders, one of the most infrequently described forms in ancient skeletons is leukemia, or the myeloproliferative neoplasms of the reticuloendothelial system affecting bone marrow and blood. This case study describes and interprets a suite of lytic and proliferative lesions in the skeletal remains of an Early/Middle Colonial-era child (ca. A.D. 1533–1620) excavated at the ruins of Eten, southwestern Lambayeque Valley Complex (north coast of Peru). A secondary burial contained the incomplete postcranial remains of a 5–6 year-old child whose bones were characterized by abnormal porous loci in the right clavicle, scapulae, long bones of the upper limb, ribs, and thoracic and lumbar vertebrae. Additionally, fine areas of new bone formation were present on the clavicle and ribs. Multiple pathological conditions were evaluated in a differential diagnosis, including taphonomic changes and various bone resorbing and forming disorders. The lesions are most consistent with acute childhood leukemia and represent the first of its kind described in Andean South America. The identification of this condition helps focus research questions involving the bioarchaeology of cancer in the Andes, especially regarding the significance of neoplastic disorders in relation to the broader reconstruction of past human health in Peru. Copyright © 2014 John Wiley & Sons, Ltd.