OBJECTIVE: To determine the prognostic value of the extent of ulceration, categorized as diameter of ulceration and as percentage of invasive melanoma diameter. BACKGROUND: Ulceration is an adverse prognostic factor for clinically localized primary cutaneous melanoma. However, the prognostic significance of the extent of ulceration remains unclear. METHODS: Clinicopathologic and follow-up data on 4661 patients treated at a single center were analyzed. RESULTS: Both the presence and extent of ulceration were independent predictors of survival. The 5-year melanoma-specific survival (MSS) for ulcerated and nonulcerated melanomas was 77.6% and 91.3%, respectively. The 5-year MSS for minimally/moderately ulcerated melanomas (=70% or =5 mm) was 80.4% and 82.7%, respectively, compared to extensively ulcerated melanomas (>70% or >5 mm), which had a 5-year MSS of 66.4% and 59.3%. On multivariate analysis, tumor thickness and the presence/absence of mitoses were the most powerful predictors of MSS. The presence of ulceration was also an independent predictor of poorer MSS (hazard ratio [HR] = 1.55, P 70%: HR = 2.20 and >5 mm: HR = 2.03). CONCLUSIONS: Extent of ulceration (measured either as diameter or percentage of tumor width) provides more accurate prognostic information than the mere presence of ulceration. This has potential implications for melanoma patients with regard to prognosis, staging, management, and eligibility for clinical trials. We recommend that extent of ulceration be recorded in pathology reports for all ulcerated primary cutaneous melanomas.