We performed a prospective study to investigate whether the sonographic appearance of the testicular parenchyma changes during maturation of the testis. One hundred forty-three boys ranging in age from 6 months to 16 years, and 11 volunteers aged about 30 years, were included in the study. The echogenicity of each of the 308 normal testes were determined by measuring the average brightness of a histogram over a defined testicular area. To avoid divergent results due to different settings of the device in individual cases, the average brightness of a histogram of a standard ultrasound phantom was measured immediately after the examination of each testicle. From these 2 measurements, testicular echogenicity could be calculated independently of individual equipment settings. All testes had a homogeneous echotexture. The echogenicity of the prepubertal testis was markedly reduced compared to the medium-level echogenicity of the mature testis (p < 0.001). Testicular echogenicity increases during puberty. We conclude that testicular echogenicity increases with maturation. Knowledge of this fact may improve the diagnostic performance of scrotal ultrasound especially in children.