We report what we believe to be the first case of high-grade, radiation-induced, intratesticular leiomyosarcoma in a 30-year-old man who had had testicular relapse of acute lymphoblastic leukemia at age 12 years that was treated with standard testicular field radiation (2400 cGy) and chemotherapy. Radiation-induced tumors of this type are rare, have a median latency of 10 years, and are usually dose dependent (around 5000 cGy). Testicular leiomyosarcoma, especially high grade, remains to be fully characterized. After radical orchiectomy, patients should be followed up with serial germ cell tumor markers and imaging to monitor for metastatic spread. The use of retroperitoneal lymph node dissection and chemotherapy remains controversial but is probably not indicated.