Sinonasal undifferentiated carcinoma (SNUC) rarely occurs in the pediatric population. Surgical resection with or without postoperative radiation or chemoradiotherapy is the gold standard for treating malignant sinonasal tumors. However, some patients may decline surgery. This paper discusses the experience of SNUC in a child who was treated with only chemoradiotherapy. A 10-year-old child presented with complaints of left-sided nasal congestion, facial asymmetry, and a growing lump on the left side of the neck over the past year. Physical examination revealed a red mass filling the left nostril. Histopathological examination of the mass confirmed a diagnosis of undifferentiated sinonasal carcinoma. The child's parents refused surgery and chose for chemoradiotherapy instead. On reassessment 3 months after the completion of therapy, the patient had achieved complete remission. Although surgery remains the primary treatment for SNUC, in certain cases, as demonstrated in this report, chemoradiotherapy alone may be a viable option.