Superior mediastinal syndrome secondary to an anterior mediastinal mass can be seen in acute lymphoblastic leukemia of T-cell lineage. We report a 3 years old child with B-cell ALL, who presented with superior mediastinal syndrome. The CT scan chest showed a huge anterior mediastinal mass and the peripheral blood immunophenotying showed B-cell acute lymphoblastic leukemia. High-risk remission induction chemotherapy was given and he achieved remission by the end of induction therapy, both in terms of medullary and extramedullary disease. This is the first reported case of a pediatric B-cell ALL presenting with the superior mediastinal syndrome.