Clues provided by evidence that susceptibility to mouse retroviral ALL is linked to the MHC [11], and that certain human leukocyte antigen (HLA) alleles are associated with susceptibility to specific infections (reviewed in [12]), have encouraged the search for HLA allele associations with childhood ALL as a proxy for infection [13], [14], [15], [16], [17]. Here, HLA-C is linked to acute lymphoblastic leukemia.