Among pediatric non-Hodgkin lymphomas, one of the most frequent types is lymphoblastic lymphoma (LBL). Specific chromosome abnormalities are associated with prognosis in childhood acute lymphoblastic leukemia, but have not been evaluated for prognostic value in pediatric LBL. For the Children's Cancer Group protocol CCG-E-08 Etiologic Study of Non-Hodgkin Lymphoma in Childhood, 13 patients were enrolled with cytogenetic analysis of LBL and on treatment protocol CCG-502. Pathology material and karyotypes at initial diagnosis were given central review. The patients were aged 6-13 years (median 9 years), with a male-to-female ratio of 12:1. All patients had advanced disease. Disease relapsed in six patients (event-free survival 54% +/- 14%, median 10.8 years). Chromosome abnormalities were identified in 11 (85%), and translocations at 14q11.2 likely involving the T-cell receptor alpha/delta locus (TCR A/D) occurred in 4 (31%). For patients with relapse, four had translocations t(1;14)(p32;q11.2), t(8;14)(q24.1;q11.2), t(11;14)(p13;q11.2), or t(9;17)(q34;q23), involving breakpoints in the regions of TAL1, MYC, LMO2, and NOTCH1, respectively. Pediatric advanced LBLs have a high frequency of chromosome abnormalities; in this limited study, these often involved translocations at 14q11.2, the site of TCR A/D. Translocations possibly involving TAL1, MYC, LMO2, or NOTCH1 may have contributed to poor outcome. Further studies are warranted in larger cohorts of children and adolescents with LBL to evaluate the prognostic significance.