This retrospective study performed by the Eastern Cooperative Oncology Group and the Southwest Oncology Group enrolled 140 acute promyelocytic leukemia (APL) patients with t(15;17) to determine the influence of additional karyotypic abnormalities on treatment outcome. Karyotypes were centrally reviewed by both study groups. The complete response rate after induction for patients with t(15;17) treated with chemotherapy, or all-trans retinoic acid (ATRA) as induction therapy was not affected by additional cytogenetic aberrations. Disease-free (DFS) and overall survival (OS) were unaffected by additional cytogenetic abnormalities if treatment was chemotherapy without ATRA. Patients with t(15;17) only, treated with ATRA with or without chemotherapy, had an improved DFS (P = 0.06) and a better OS (P = 0.01) compared with ATRA-treated patients with additional cytogenetic abnormalities. Patients with APL and t(15;17) alone are significantly more sensitive to treatment with ATRA than are patients with t(15;17) and additional cytogenetic abnormalities.