Q- and C-banded karyotypes of leukemic cells of a patient with congenital acute lymphoblastic leukemia showed the karyotype: 46,XX,ins(6;1)(p21;p13p36). This rearrangement is unusual, and the breakpoints on chromosome 1 are interestingly close to known cellular oncogenes (N-ras, fgr, src-2) and to a putative antioncogene.