Primitive myxoid mesenchymal tumor of infancy is a rare, locally aggressive, chemotherapy-refractory pediatric sarcoma with a high morbidity and mortality rate. Surgical resection is the gold standard of treatment, but a significant number of cases are initially unresectable due to tumor location. For these individuals, traditional first-line chemotherapy with vincristine, actinomycin, and cyclophosphamide has yielded no benefit. Alternatively, therapy with doxorubicin and ifosphamide-based regimens have shown success in several cases. We present a case of a pediatric patient with unresectable PMMTI successfully cured after receiving a combination of ifosphamide and doxorubicin followed by surgery and adjunctive proton beam radiation.