In acute lymphoblastic leukemia, besides age and white cell count at diagnosis, the cytogenetic abnormalities t(9;22)/BCR-ABL and t(4;11)/MLL-AF4 are important prognostic markers and are often included in the treatment stratification of patients with adult acute lymphoblastic leukemia. Deletions in 9p are seen in about 9% of cases of adult acute lymphoblastic leukemia, but their prognostic impact has been controversial. Cytogenetic data from 381 patients diagnosed with B-precursor acute lymphoblastic leukemia were reviewed. Chromosomal analysis was successful in 240 cases. Of these cases, 18 (8%) had abnormalities in 9p and they were compared with patients with normal karyotypes and patients with t(9;22)/BCR-ABL. Patients with abnormalities of chromosome 9 showed significantly shorter overall survival compared with patients with normal karyotypes. In fact, overall survival was similar to that in the poor prognosis t(9;22)/BCR-ABL-positive group. Our data suggest that chromosomal abnormalities involving 9p may have a significant negative impact on survival in adult B-precursor acute lymphoblastic leukemia.