Type B lactic acidosis (LA) is a distinct form of metabolic acidosis characterized by low blood pH (≤ 7.35) accompanied by accumulation of lactate (blood concentration ≥ 5 mmol/L) (Luft et al. in Am J Clin Pathol 80:484-489, 1983). There are two types of LA that are caused by different mechanisms. Type A is more common, and is caused by the lack of oxygen (tissue hypoxia or hypoperfusion). In this case, impaired cellular respiration leads to lower pH level and at the same time the cells are forced to metabolize glucose anaerobically, which leads to increased production of lactate. The other type, Type B, is relatively rare, and is occasionally found in patients with hematological malignancies, such as leukemia or lymphoma. The molecular mechanism of Type B LA is not fully understood. Here, we report a case of precursor B cell acute lymphoblastic leukemia who initially shows manifestations of Type B LA and bilateral renal enlargement.