Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy and its prognosis has considerably improved over the past 2 decades due to new therapeutic approaches. In some cases, however, it can develop very rapidly and cause possibly fatal complications. We report on the case of an 11-year-old boy with ALL, who rapidly developed severe lactic acidosis and abdominal compartment syndrome. He died of multiorgan failure only 5 days after diagnosis of ALL had been established. Autopsy revealed systemic leukemic infiltrations. We suppose that the mass of tumor cells induced a cascade of metabolic and endocrine reactions, which not only triggered the rapid progression of the disease but were also accountable for the lack of response to treatment. The pathophysiology of abdominal compartment syndrome as a rare and in our case ultimately fatal complication of ALL is described.