Primary testicular lymphoma (PTL) is a rare extranodal malignancy arising from the testis, accounting for approximately 5% of all testicular tumors and 1–2% of non-Hodgkin lymphomas, with diffuse large B-cell lymphoma being the predominant histological subtype. It is typically described as a disease of elderly males, whereas testicular tumors in younger individuals are more commonly non-seminomatous germ cell tumors, often associated with elevated tumor markers such as alpha-fetoprotein and beta-human chorionic gonadotropin. We report a case of a 40-year-old man who presented with painless, progressively enlarging bilateral testicular swelling over a period of 2–2.5 months. Clinical examination revealed enlarged, non-tender testes bilaterally. Ultrasonography demonstrated bilateral testicular enlargement with diffuse heterogeneous echotexture, particularly involving the right testis measuring 6 × 3.6 cm, suggestive of diffuse pathology. Notably, tumor markers were within normal limits, posing a diagnostic challenge. The patient underwent bilateral high inguinal orchiectomy, and histopathological evaluation confirmed non-Hodgkin lymphoma. PTL is an aggressive malignancy with limited data guiding its management due to its rarity; however, orchiectomy remains both diagnostic and therapeutic, and early initiation of systemic therapy is recommended. This case is noteworthy for its atypical presentation with bilateral synchronous involvement, occurrence in a relatively younger patient, and absence of tumor marker elevation, mimicking seminomatous pathology and contributing to diagnostic ambiguity.