The identification of genetic risk subgroups of T-cell acute lymphoblastic leukemia (T-ALL) may provide evidence for risk stratification and individualized treatment. We investigated the characteristics and prognostic value of tumor suppressor gene CDKN2A deletions in 101 patients with T-ALL. CDKN2A deletion was present in 23% (23/101) of T-ALL by fluorescence in situ hybridization (FISH). The most common type of CDKN2A deletion was homozygous deletion (70%, 16/23). A lower frequency of CDKN2A deletion was found in patients with early T-cell precursor (ETP) ALL than in patients with non-ETP-ALL (10.4% vs. 34.0%; P=0.008). Deletion of CDKN2A was significantly associated with younger age (P=0.001), higher white blood cell (WBC) count (P<0.001) and higher lactate dehydrogenase (LDH) level (P=0.002). Patients with CDKN2A deletion had lower 2-year overall survival (OS) and event-free survival (EFS) rates than patients without CDKN2A deletion (2-year OS: 18.6%±8.9% vs. 47.4%±6.2%, P=0.032; EFS: 16.4±8.3 vs. 38.6±5.9%, P=0.022). In multivariable analysis, CDKN2A deletion was an independent adverse prognostic factor for OS (P=0.016). In conclusion, adult T-ALL patients with CDKN2A deletion had a poor prognosis, and these patients might benefit from intensive chemotherapy or allogeneic hematopoietic stem-cell transplantation. This article is protected by copyright. All rights reserved.