To reveal the relationship between hypodiploidy with 30 to 39 chromosomes and near-triploidy in acute lymphoblastic leukemia (ALL), we studied 24 patients presenting with one of these aneuploidies among 623 adults with ALL registered in the Leucemie Aigue Lymphoblastique de l'Adulte (LALA) protocols. The 2 ploidy groups presented a striking similarity of their cytogenetic profiles: chromosomes 2, 3, 4, 7, 13, 15, 16, and 17, significantly monosomic in hypodiploidy 30 to 39, were also frequently disomic in near-triploidy, whereas those retained in pairs in hypodiploidy 30 to 39 were frequently tetrasomic in near-triploidy. DNA content data revealed the simultaneous presence of 2 aneuploid peaks in most tested cases (DNA indexes: 0.72-0.87/1.39-1.89) and a multiple correspondence analysis applied on cytogenetic profiles ascertained their strong relationship. We thus assumed that near-triploidy derives from the duplication of hypodiploidy with 30 to 39 chromosomes and that both aneuploid groups are 2 expressions of the same disease. These 24 patients presented with B-cell phenotype, low leukocytoses (median white blood cell count, 4.2 x 10(9)/L), and poor prognosis (complete remission, 57%; median disease-free-survival, 8 months; median survival, 10.4 months) comparable to that of Ph(+) patients treated according to the same protocol. We suggest that hypodiploidy with 30 to 39 chromosomes or near-triploidy should be regarded as a new high-risk factor in the risk stratification of adult ALL protocols.