Although well recognized in the literature, the contemporary clinicopathologic data regarding choriocarcinoma (CC) as a pure or the predominant component of a testicular germ cell tumor (GCT) are limited. Herein, we present a series of pure CC and predominant CC in mixed GCT of the testis obtained from a single oncology institution. A comprehensive histologic review of 1010 orchiectomies from 1999 to 2011 yielded 6 (0.6%) pure CC and 9 (0.9%) mixed GCT cases with a predominant CC component. Patients' ages ranged from 20 to 39 years (median 29 y). All patients had markedly elevated serum β-hCG levels (median 199,000 IU/mL) at presentation. All tumors were unilateral and involved the right (9/15) and left (6/15) testis. The mean tumor size was 6.5 cm (range, 1.5 to 8 cm). Histology was similar for pure CCs and the CC component of mixed GCTs. CC commonly showed expansile hemorrhagic nodular cysts surrounded by variable layers of neoplastic trophoblastic cells (mononucleated trophoblasts and syncytiotrophoblasts). The syncytiotrophoblasts usually covered columns of mononucleated trophoblasts and occasionally formed plexiform aggregates and pseudovillous protrusions. Immunohistochemical stains suggested a mixture of cytotrophoblasts (p63, HPL) and intermediate trophoblasts (p63, HPL weak +/-) in the columns of mononucleated cells. In the 9 mixed GCTs, CC comprised 50% to 95% (7/9 were ≥80% CC) of the tumor; 7 were combined with 1, and 2 were combined with 2 other GCT components. The non-CC components included teratoma (5/9), seminoma (2/9), yolk sac tumor (2/9), and embryonal carcinoma (2/9). Lymphovascular invasion, spermatic cord invasion, and tunica vaginalis invasion were present in 15/15, 5/15, and 1/12 cases, respectively. In mixed GCTs, these locally aggressive features were attributed to the CC component, except in 1 tumor in which it was also exhibited by the embryonal carcinoma component. Lymphovascular invasion was multifocal to widespread in 73% of tumors. The stages of the 15 tumors were: pT2 (10), pT3 (5); NX (1), N1 (4), N2 (5), N3 (5); and M1a (2) and M1b (13). Distant organ metastasis mostly involved the lungs (11) and liver (10). Follow-up information was available in 14 patients, all of whom received cisplatin-based chemotherapy. All 6 pure CC patients were dead of disease (range, 6 to 14 mo, median 9.5 mo). Follow-up of 8 patients with predominant CC (range, 10 to 72 mo, median 27 mo) showed that 5 died of the disease, and 1 was alive with disease and 2 were alive with no evidence of disease at 60 and 72 months of follow-up, respectively; these latter 2 patients were the only ones with M1a disease on presentation. This series confirms the proclivity for high-stage presentation including presence of distant metastasis, hematogenous spread, and poor outcome of testicular CC. Mixed GCT with a predominant CC component has similar tendency for high-stage presentation, marked elevation of serum β-hCG levels, and aggressive behavior compared with pure CC. This study also showed that distant metastasis by CC when only involving the lungs (M1a) may not be uniformly fatal with chemotherapy. The mononucleated trophoblastic columns in testicular CC appear to be a mixture of cytotrophoblasts and intermediate trophoblasts, similar to that described in gestational CC.