Is it normal for one testicle to be larger than the other?

The testes undergo rapid growth during sexual maturation and gradually atrophy and shrink with advancing age as sexual function declines. The surface of each testis is covered by a dense, fibrous capsule known as the tunica albuginea. Along the posterior border of the testis, this tunica albuginea thickens and projects inward to form the mediastinum testis. Some men may present with asymmetrical testicular size—i.e., one testicle noticeably larger than the other. Is such asymmetry normal? Below, we address this question.

Is it normal for one testicle to be significantly larger than the other?

In general, slight asymmetry in testicular size among adult males is common and considered physiologic. However, marked disparity in size is abnormal and warrants medical evaluation. Patients should consult a healthcare provider to rule out conditions such as cryptorchidism (undescended testis) or hydrocele (testicular鞘膜积液). Typically, cryptorchidism results in one testicle being smaller than normal, whereas a hydrocele causes enlargement of one testicle. Thus, either condition may manifest as unilateral testicular enlargement or reduction in size. Additionally, the testes reside within the scrotum—one on the left and one on the right—with the left testis usually positioned approximately 1 cm lower than the right. Each testis is slightly flattened and oval-shaped, with a smooth surface. It possesses medial and lateral surfaces, anterior and posterior borders, and superior and inferior poles. The anterior border is free, while the posterior border contains vessels, nerves, and lymphatic vessels entering and exiting the testis, and is adjacent to the epididymis and the testicular portion of the vas deferens. The superior pole and posterior border are covered by the head of the epididymis; the inferior pole is free. The lateral surface is more convex, whereas the medial surface is relatively flat. Consequently, testicular size increases rapidly during sexual maturation and diminishes progressively with aging and declining sexual function.

Knowledge Extension: What Causes Hydrocele?

1. Primary Causes

The etiology of primary (idiopathic) hydrocele remains incompletely understood. It may result from increased secretion or decreased absorption of fluid by the tunica vaginalis, or from congenital anomalies—such as developmental defects in the lymphatic channels of the tunica vaginalis cavity—or from subclinical or previously resolved epididymo-orchitis. In contrast, secondary hydroceles commonly arise following inflammation or infection (e.g., orchitis, epididymitis, tuberculosis), filariasis of the scrotum, testicular neoplasms, scrotal surgery, or trauma. The fluid in secondary hydroceles often contains white blood cells.

2. Underlying Diseases

Acute inflammatory conditions—including acute orchitis, epididymitis, and funiculitis—can stimulate excessive transudation from the tunica vaginalis, leading to acute hydrocele formation. Scrotal surgery may damage lymphatic vessels, impairing lymphatic drainage; similarly, systemic conditions such as high fever, heart failure, or ascites may precipitate acute hydrocele. Chronic secondary hydroceles are frequently associated with chronic orchitis or epididymitis, syphilis, tuberculosis, or testicular tumors—conditions that promote increased fluid secretion by the tunica vaginalis. Moreover, parasitic infections such as filariasis and schistosomiasis can also cause hydrocele.

The above provides an overview of whether asymmetrical testicular size is normal. We hope this information is helpful to you.