BACKGROUND: Body composition has emerged as a significant determinant of cancer patient outcomes, with computed tomography (CT) assessment at the L3 level offering a reliable evaluation method. While muscle mass and adiposity have been linked to poorer outcomes in hematological malignancies, their impact remains unstudied in adults with acute lymphoblastic leukemia (ALL). METHODS: This retrospective single-center study enrolled adults newly diagnosed with ALL. Skeletal muscle, visceral, and subcutaneous fat areas were quantified. Low muscle mass was defined as a skeletal muscle index (SMI) less than 55 cm RESULTS: Ninety patients were included. Low muscle mass was associated with mortality in patients treated with a pediatric inspired regimen (PIR) (HR 4.92, 95 % CI [1.38-17.57], p = 0.014) and lower median SMI was observed in patients who died during induction (p = 0.016). High visceral adiposity (HR 1.89, 95 % CI [1-3.57], p = 0.049) and high subcutaneous adiposity (HR 1.99, 95 % CI [1-3.96], p = 0.05) were also associated with mortality in the whole population. Furthermore, a higher VATI was observed in patients who developed an infectious episode during induction (p = 0.03), and a higher VATI was observed in patients who were treated with a PIR who had measurable residual disease positivity after induction chemotherapy (p = 0.044). CONCLUSION: CT-assessed muscle mass, and adiposity bear prognostic significance in newly diagnosed ALL patients.