Objectives. To report the initial experience with sentinel node identification using the gamma probe in patients with intermediate-risk penile cancer (T2NXM0, or T1 with intermediate or high-grade disease) and impalpable groin nodes.

Methods. Technetium-99m-labeled sulfur colloid was injected at the site of primary penile carcinoma 1 hour before surgery. The sentinel lymph nodes were located using the gamma probe and excised through a 3-cm inguinal incision. A full groin dissection was performed only in cases in which frozen section of the node demonstrated metastasis.

Results. Nine sentinel nodes were identified by the gamma probe and excised in 5 men. In 3 patients, the sentinel nodes were negative bilaterally. In 2 patients, the sentinel node, although grossly normal, showed a single focus of metastasis by frozen section analysis. In both of these patients, a full groin dissection was carried out and revealed no other nodal metastases. All 5 remained free of recurrence (median follow-up 18 months, range 16 to 23).

Conclusions. In patients with microscopic involvement of a single lymph node only (confirmed by full groin dissection), gamma probe identification was 100% accurate. None of the patients with negative sentinel nodes had a recurrence. Biopsy of the sentinel nodes using the gamma probe can predict the presence or absence of inguinal node metastasis in patients with intermediate-risk penile cancer, sparing many patients the long-term morbidity of a full groin dissection. These initial results suggest further study is warranted.