Cytogenetic analysis was performed in 30 patients with T cell acute lymphoblastic leukemia (11 adults, 19 children) at initial presentation and analysis was also repeated in clinical and hematological remission in 15 patients. At initial presentation, chromosomal abnormalities were detected in 27 cases (90%) and hypodiploidy was detected in 19 patients (63.3%), followed by pseudodiploidy in six patients (20%) and hyperdiploidy in two patients (6.6%). Other karyotypic abnormalities detected were deletion 6q (40%), deletion 11 q (16.6%), deletion 7q (10%), abnormalities of chromosome 9 in (13.3%) and translocation t(11;14)(p13;q11) in 6.6% and der(12)t(12;?)(p13;?) in (3.3%). In complete remission, nine out of 15 cases (60%) showed chromosomal aberrations. Original abnormalities were detected in two cases (13.3%) and new abnormalities were detected in seven cases (46.6%).