Purpose The purpose of this study was to describe the ultrasonographic findings of testicular atrophy after mumps orchitis. Methods We retrospectively reviewed the case files of eight patients (14 to 24 years old; mean, 17 years) with mumps orchitis and testicular atrophy who were treated between January 2011 and September 2017. On gray-scale and color Doppler, the ultrasonographic features of volume, shape, echogenicity, and degree of blood flow in the testes were analyzed as part of both initial and follow-up ultrasonography. The duration between the initial diagnosis of mumps orchitis and the ultrasonographic diagnosis of testicular atrophy after mumps orchitis ranged from 25 to 230 days (mean, 95.9 days). Results Of the eight patients with testicular atrophy after mumps orchitis, the testes were affected unilaterally in seven patients (6 right-sided and 1 left-sided) and bilaterally in one patient. The affected testes (n=9) were 23%-55% (mean, 44.7%) smaller in volume (mean, 6.3±2.0 mL) than the contralateral normal testes (n=7) (mean, 10.8±2.3 mL) on follow-up ultrasonography (P=0.001). The shape of the atrophic testes was oblong in seven cases and elliptical in two cases. The atrophic testes were either heterogeneously hypoechoic with multiple hyperechoic islands (n=7) or heterogeneously hyperechoic (n=2). On follow-up color Doppler ultrasonography, the degree of vascularity of the atrophic testis was either similar to (n=3) or lower than (n=6) that of the contralateral testis. Conclusion On ultrasonography, atrophic testes after mumps orchitis tended to exhibit an oblong shape, heterogeneous low echogenicity with multiple hyperechoic islands, and decreased vascularity.