This is a retrospective review of 62 patients with Stage II testicular seminoma treated either by initial radiation therapy (48 patients) or by platinum-containing chemotherapy (14 patients). For all 62 cases, disease-free survival from 2 to 20 years was 86%, uncorrected survival was 86% at 5 years and 83% at 15 years, and survival corrected for deaths from intercurrent disease was 90% from 2 to 20 years. There were no significant differences in outcome between the two treatment groups. An analysis of potential prognostic factors for the initial radiation therapy group and for the whole group revealed that age, site of primary, cryptorchidism, ipsilateral hernia repair, contralateral testicular atrophy, scrotal incision, elevated postorchiectomy beta-human chorionic gonadotropin level, epididymal invasion, spermatic cord involvement, and vascular invasion in the primary were not significant. However, bulk of abdominal disease was a prognostic factor. Patients with small-volume abdominal disease defined as nonpalpable disease or as a mass less than 10 cm in largest diameter accounted for two-thirds of the series and had a disease-free survival of 95% when treated with initial radiation therapy. Patients with bulky disease, either palpable or greater than or equal to 10 cm in diameter, had a disease-free survival of 64%. The relative roles of the two treatments in bulky abdominal disease are discussed, but in the absence of a prospective study it is not possible to definitively answer the question of which modality is best in this setting. In our series, the patients treated with platinum-containing chemotherapy fared as well as the primarily irradiated patients, but 71% of the former had palpable masses, compared with 22% of the latter. The chemotherapy-treated patients who relapsed were treated with radiation therapy for salvage, leading to a 100% survival corrected for intercurrent death. We have therefore elected to continue the policy of initial radiation therapy for small-volume (less than 10 cm) disease and platinum-containing chemotherapy for bulky disease (greater than or equal to 10 cm), with irradiation used for residual masses.