The prognostic relevance of the extent of nodal metastases, lesion thickness, level of invasion, site of lesion, satellitosis, age, sex, and year of diagnosis and treatment were assessed in 213 consecutive patients with pathologic Stage II malignant melanoma (157 with clinical Stage I disease and 56 with clinical Stage II disease). Of these factors, only three were significant: 1) clinical status of the lymph nodes (p less than 0.0001); 2) thickness of the primary lesion in the ranges of less than 2.0 mm, 2.0 to 4.9 mm, and 5.0 mm or greater (p = 0.002); and 3) level of invasion (p = 0.0002). The extent of nodal metastases in those patients with clinical Stage I disease was not significant. The difference in survival between patients with clinically negative/histologically positive nodes (clinical Stage I) and clinically positive/histologically positive nodes (clinical Stage II) was apparent throughout the follow-up period. The 5- and 10-year survival rates for the clinical Stage I patients were 44% and 28%, respectively, and for the clinical Stage II patients 21% and 12%, respectively (p less than 0.0001). A 5-year cumulative survival rate of 65% was achieved for clinical Stage I patients having primary lesions of less than 2.0 mm in thickness, while it was 19% for patients having primary lesions of 5.0 mm or more in thickness. For pathologic Stage II malignant melanoma patients, prognosis is most dependent on the clinical status of the lymph nodes, not on the number of lymph nodes with micrometastases.