We describe an 18-year-old man with acute leukemia who presented with posterior reversible encephalopathy syndrome (PRES) shortly after developing acute pancreatitis. On day 15 after the third consolidation course with high-dose cytarabine, treatment with broad-spectrum antibiotics was initiated for febrile neutropenia. On day 16, he developed septic shock, and subsequently, acute respiratory distress syndrome (ARDS). After adding vancomycin, micafungin and high-dose methylprednisolone (mPSL) to his treatment regimen, these manifestations subsided. On day 22, he received hemodialysis for drug-induced acute renal failure. On day 24, he developed acute pancreatitis possibly due to mPSL; the following day he had generalized seizures, and was intubated. Cerebrospinal fluid findings were normal. Brain MRI revealed hyperintense signals on FLAIR images and increased apparent diffusion coefficient values in the sub-cortical and deep white matter areas of the bilateral temporal and occipital lobes, indicative of vasogenic edema. Thus, we diagnosed PRES. Blood pressure, seizures and volume status were controlled, with MRI findings showing improvement by day 42. He was extubated on day 32 and discharged on day 49 without complications. Although little is known about PRES following acute pancreatitis, clinicians should be aware that this condition may develop.