Acute lymphoblastic leukemia (ALL) is the most common of all childhood malignancies. Current remission rates approach 80%. Recurrent disease can present in a wide variety of ways. MR imaging plays a crucial role in the detection of disease relapse. Because other disorders can mimic recurrence of leukemia, it is important for the radiologist to judge recurrence from non-recurrence accurately in order to avoid unnecessary testing and emotional stress on the patient and family.