Here, we report the use of a methylene blue oral rinse for the treatment of oral mucositis--associated pain. A child receiving chemotherapy for acute lymphoblastic leukemia had progressive decline in clinical condition from uncontrolled oral pain associated with mucositis. Conventional therapy was shown to be ineffective and eventually discontinued. The patient received a methylene oral rinse treatment, which provided good pain control and allowed him to recover successfully completing his chemotherapy. The use of the methylene blue oral rinse can be a safe, inexpensive, and effective treatment for mucositis-related oral pain in the pediatric cancer patient population.