A 13-year-old boy was referred to the authors' hospital following a right inguinal orchiectomy for a right scrotal mass. Histopathological examination revealed Burkitt lymphoma. The left testis was found to be small with heterogeneous parenchyma by scrotal ultrasound (US) and other systemic investigations were negative for lymphoma involvement. Ultrasound-guided fine-needle aspiration biopsy showed no evidence of involvement in the left testis. Considering stage I Burkitt lymphoma, chemotherapy was started. Following the first course, US findings changed: the volume of the left testis decreased and the parenchyma became homogeneous. The left testis was considered to be involved by lymphoma at initial diagnosis and chemotherapy was intensified. At the end of 5 months of chemotherapy the left testis was again heterogeneous in US. A wedge-biopsy was negative for lymphoma. The patient is under regular follow-up and is in complete remission 19 months after the end of chemotherapy. Primary testicular lymphoma is quite rare in children and experience is limited. Changes in testicular size and parenchyma by US should not necessarily indicate involvement by lymphoma in pubertal boys.