The aim of the present study was to analyze chromosome abnormalities in Korean patients with T-cell acute lymphoblastic leukemia (T-ALL). A total of 65 patients with newly diagnosed T-ALL were enrolled in the study from December 2004 to December 2011. Chromosome analysis was performed at diagnosis on short-term cultures of bone marrow specimens. Of these 65 patients, abnormal karyotypes were found in 50 (77 %). Numerical and structural chromosome abnormalities were identified in 16 (25 %) and 47 (72 %) patients, respectively. Deletion was the most common structural abnormality (48 %), followed by translocation (29 %). Overall survival (OS) and relapse-free survival (RFS) outcome were unaffected by the number and/or type of chromosome abnormalities in both childhood and adult T-ALL; however, the OS interval was longer for childhood patients than for adult patients in the entire cohort (P = 0.0003). Similarly, patients with first complete remission (CR) showed a better OS than those who failed to achieve first CR (P < 0.0001). There was a negative clinical impact in adult patients and patients without first CR according to multivariate analysis. This study helps to fill the gap regarding chromosome findings in T-ALL and may lead to identification of the molecular background behind phenotypic differences.