For 16 dogs with testicular neoplasia (n = 19 tumors), ultrasonography was performed to determine whether a correlation exists between ultrasonographic features of testicular tumors and cell type. The echogenicity of the tumors varied depending on the size of the tumor and whether the tumor had focal or diffuse distribution within the testis. The ultrasonographic characteristics of Sertoli cell tumors were variable, with no predominant pattern. This variation may be related to tumor size, because 6 of 7 Sertoli cell tumors were greater than 5 cm in diameter. Focal seminomas and interstitial cell tumors less than 3 cm in diameter had hypoechoic texture. Focal seminomas and interstitial cell tumors greater than 3 cm in diameter had mixed echogenicity. Tumors of multiple cell types were greater than 5 cm in diameter and had mixed echogenicity. In valuable breeding dogs with a small (less than 3 cm) focal intrascrotal lesion, testicular ultrasonography would be of benefit for localization of the mass to the testis or epididymis for subsequent biopsy. In dogs with intraabdominal neoplastic testes, ultrasonography may be of benefit in determining intra-abdominal metastases and invasion of contiguous structures.