Type I Chiari malformation (CM-I) consists of downward herniation of the cerebellar tonsils below the foramen magnum and often requires surgical decompression if symptomatic. Spontaneous resolution of CM-I is rare. We present a case of resolved CM-I without surgery in a 6-year-old boy with B-cell lymphoma who was diagnosed with CM-I during lymphoma staging. Cerebrospinal fluid cytology and brain MRI revealed negative CNS involvement but showed CM-I with tonsillar ectopia 19 mm below the foramen magnum. The patient underwent induction chemotherapy including 5 doses of intrathecal chemotherapy. Follow-up MRI demonstrated marked regression of CM-I to less than 6 mm in 3 months, and complete resolution of CM-I was observed in 2 years. To the best of our knowledge, this is the first case of resolved CM-I and syringomyelia following chemotherapy. In this case report, the authors summarize all of the clinical characteristics, the radiological appearance, and the potential causes of resolution based on a review of the literature and propose the mechanisms through which intrathecal chemotherapy contributed to the CM-I and syringomyelia resolution in the present case.