Splenic marginal zone lymphoma (SMZL) comprises about 1% of B-cell lymphomas and typically occurs after the age of 50 years. Pediatric SMZL is very rare, and no FDG PET/CT imaging of the disease has been reported. In the current study, a 4-year-old boy with biopsy-proven SMZL had FDG PET/CT for staging, which showed increased metabolic activity in the spleen and left cervical lymph nodes. A second FDG PET/CT for evaluation of treatment response showed complete resolution of abnormal FDG uptake in the nodes and spleen with decrease in size of the nodes.