BACKGROUND T-cell acute lymphoblastic leukemia (T-ALL) accounts for approximately 10-13% of childhood ALL cases. Patients with T-ALL frequently present with unfavorable features at diagnosis and thus are considered to have a higher risk to relapse. Within the last 10 years, the previously dismal prognosis of this ALL subtype has been improved by intensified chemotherapy. However, 30-40% of patients still relapse, so that additional prognostic factors such as the local response of the mediastinal mass to therapy might allow defining the patients at risk in a better manner. METHODS A retrospective analysis of 116 Austrian patients with T-ALL was performed to assess whether an initial mediastinal mass (70/116) and its response to chemotherapy as measured by thoracic X-rays (32/70) might predict outcome. RESULTS Neither patients with a mediastinal tumor at the time of diagnosis nor patients with an incomplete response on day 35 or 70 of therapy had a worse prognosis, as compared with the group of patients with no initial tumor and complete regression on day 35 and 70. CONCLUSIONS We failed to show that in children with T-ALL residual mediastinal tumors are of prognostic relevance. This might suggest that incomplete local response is not necessarily an indication for treatment intensification such as local irradiation, second-look operation, or high-dose chemotherapy with bone marrow rescue. However, due to the relatively small number of patients analyzed, our results have to be validated prospectively on a larger cohort of patients in future clinical trials.