From 1958 through 1969, inclusive, 418 patients with melanoma of the trunk were treated at the M. D. Anderson Hospital and Tumor Institute. Of these, 128 patients (31%) had Stage I disease and were treated by excision with observation of regional nodes in all except five patients. Retrospectively these Stage I patients were analyzed regarding (1) survival, (2) sites and timing of treatment failures, (3) the relation of the primary site to eventual nodal metastasis, and (4) the variables of sex, size, and location on the trunk, which also were correlated with disease control. The results show: (1) actuarial survival rate of 65.7% and 55.7% at 5 and 10 years, respectively; (2) positive regional lymph nodes (RLN) evolved in 34 patients (28%), systemic metastases in 18 patients (15%), local recurrence (LR) in four patients, LR plus RLN in one patient, and intransit metastases in three patients as the first evidence of failure. Over 90% of LR and positive RLN developed within 24 months. Many intransit recurrences and systemic metastases occurred later and account for much of the biologic variability attributed to melanomas: (3) the anatomy of the lymphatics of the trunk as described by Sappey is an excellent guide to the site of first nodal metastasis, (4) a midline or near-midline primary site correlated with regional failure (p less than 0.05). More men failed regionally than did women (p less than 0.05). In retrospective calculation, 184 regional node dissections would have been required for probable salvage of 13 patients (10%) if surgical treatment for subclinical disease had been used routinely.