Testicular infiltration developed in 6 of 56 boys with lymphoblastic leukemia. All exhibited platelet counts under 100,000, indicating poor prognosis. Patients were treated with vincristine, prednisone, and craniomemingeal prophylaxis (2,400 rads/12 fx) extending to the C2 level. Only 3 patients did not suffer recurrence of testicular disease during their multiple leukemic relapses. Alternate treatment courses are suggested.