From 1970 to 1979, a group of 50 patients was treated for squamous cell carcinoma of the penis by interstitial irradiation using an afterloading technique and iridium 192 wires. The group included 9 patients with T1 tumors, 27 with T2 tumors, and 14 with T3 tumors. Forty-five patients presented with no metastatic inguinal nodes (N0), 3 patients with N1 nodes, and 2 patients had N3 nodes. After treatment, 11 patients (1 T1, 6 T2 and 4T3) developed local recurrences; 10 of these 11 patients underwent penile amputation which controlled the tumor in 7 of the patients. One patient refused amputation. Three patients developed post-therapeutic necrosis which necessitated partial amputation in 2 cases. Eight patients developed post-therapeutic urethral stenosis, which required surgical treatment in three of the cases. Overall, at their last follow-up examinations, 74% of the patients were free of disease with conservation of penile morphology and function. Most patients without metastatic nodes (37/45) at diagnosis did not receive prophylatic treatment of the groin. Two of these patients developed delayed metastatic nodes; one was successfully salvaged. All 5 patients presenting with metastatic nodes at diagnosis died, four with uncontrolled regional disease. Twenty-one percent of the patients died of their disease. We advocate interstitial irradiation using iridium 192 wires for the treatment of non-infiltrating or moderately infiltrating squamous cell carcinoma of the penis in which the largest dimension does not exceed 4 cm. Pre-implant circumcision and regular long-term follow-up are necessary. More extensive tumors are better managed surgically. When regular follow-up can be assured, it is reasonable to forgo prophylactic treatment of the inguinal nodes in patients presenting without groin metastasis.