Risk factors associated with local recurrences were analyzed from a series of 3445 clinical Stage I melanoma patients. In single-factor analysis, tumor thickness, ulceration, and increasing age were highly significantly predictive of recurrence (p less than 0.00001). After 5 years of follow-up, local recurrence rates were 0.2% for tumors less than 0.76 mm thick, 2.1% for tumors 0.76 to 1.49 mm thick, 6.4% for tumors 1.5 to 3.99 mm thick, and 13.2% for tumors 4.0 mm or greater in thickness. Ulcerated melanomas recurred more often than nonulcerated lesions (11.5% versus 1.9%). When analyzed as a continuous variable, increasing age increased the risk of local failure. In multifactorial analysis, all of these three factors remained independently predictive of local recurrence. Recurrences were more common with nodular melanomas (5.6%) compared to superficial spreading (2.5%) or lentigo maligna melanoma (2.5%), but this difference did not reach statistical significance (P = 0.115). Lower extremity (4.7%) and head and neck lesions (4.4%) recurred more frequently than upper extremity (1.6%) or trunk (1.2%) melanomas (P = 0.0217). The highest recurrence rates were observed in patients with melanomas located on the foot (11.6%) and hand (11.1%). The safety of conservative margins for the excision of low-risk melanomas was demonstrated in a review of 1151 consecutive patients with melanomas less than 1 mm thick where only one local recurrence was observed. Sixty-two percent of these patients had resection margins of 2 cm or less. In 95 patients local recurrence developed as the first site of relapse and were treated with surgical excision. The median survival for this group was 3 years, whereas 20% of this group survived 10 years. These data demonstrate that: (1) the risk of local recurrence rises with increasing tumor thickness, presence of ulceration, and age; (2) melanomas less than 1 mm thick have a very low local recurrence rate, even when excised with margins of 2 cm or less; and (3) local recurrence is a poor prognostic sign because regional and systemic metastases subsequently develop in many patients.