At the beginning of a lymphogenous metastasizing process in malignant melanomas, the first tumor cells are found in the so-called sentinel lymph node (SLN), defined as the first tumor-draining lymph node. Its removal and histopathological examination enable us to discover metastases of malignant melanomas long before their possibility of detection by any other method. Since the beginning of 1995, we have performed more than 350 gamma-probe-guided sentinel lymphonodectomies (gamma-SLNE), without any clinical evidence of metastases as determined by lymphoscintigraphy. Using gamma-SLNE, the detection and excision of the SLN succeeded in nearly all patients. The SLNs were fixed in formalin, completely cut into 1-mm thin slices and stained for routine H&E histology and with S-100 and HMB-45. In persons with melanomas thinner than 0.75 mm, we never found micrometastases. However, the SLNs were positive in melanomas from 0.76 to 1.50 mm in about 7% of patients, in melanomas from 1.51 to 4.00 mm in about 21% and in tumors thicker than 4 mm in about 44%. In primary melanomas with satellite or in-transit metastases, the SLNs contained metastases in 75% of patients. Normally, a radical lymph node dissection (RLND) follows, as it is considered to be the necessary consequence following detection of tumor cells. The lymph nodes of the RLNDs contained further metastases in about 30% of patients. The probability of the involvement of lymph nodes other than the SLN correlates with the extension of tumor cells in the SLN. During our 4-year-follow-up, we observed only a single lymph node recurrence in a patient with a negative SLN (false negative rate of about 0.4%). The development of systemic metastasis correlates not only with the Breslow tumor thickness, but also with the extent of the involvement of the melanoma metastasis in the SLN. Summarizing, it can be said that gamma-SLNE has revolutionized melanoma surgery. Based on our data, it is absolutely necessary in the staging of malignant melanoma. In our opinion, the existing classification systems for staging lymph node involvement have to be revised in light of the results of SLNE.