The fourth case of zoonotic Dirofilaria immitis infection in a California resident is reported. This case was unique in that it involved the spermatic cord, produced significant symptoms, and upon physical examination was suspected of being an incarcerated inguinal hernia. At surgery frozen sections were inconclusive regarding neoplasia and cord involvement precluded removal of the mass without orchiectomy, which was done. Histopathology revealed a well-preserved immature male D. immitis, the canine heartworm, in a branch of the spermatic artery. The morphological identification of the worm was confirmed by polymerase chain reaction (PCR) studies. This case illustrates that D. immitis infections can complicate differential diagnosis of extrapulmonary lesions and suggests that the public health significance of this vector-borne filarial worm needs to be evaluated through appropriate epidemiological studies in enzootic areas.