The authors report the case of a 16-year-old boy with pre-B cell acute lymphocytic leukemia diagnosed 2 weeks earlier. On workup for diffuse headaches he was found to have 10-mm bilateral subdural hygromas with compression of the underlying gyri. He was followed clinically, and 4 days after his initial presentation he underwent MRI studies of the brain, which showed complete resolution of the subdural fluid collections. No change in management was noted during these 4 days. This case is the first known instance of rapid, spontaneously disappearing bilateral subdural hygromas in a pediatric patient.