Background: Epiluminescence microscopy is a useful tool for the noninvasive diagnosis of malignant melanoma based on criteria that have been correlated with specific histologic characteristics. Previous studies have also shown a good correlation between the frequency of some dermatoscopic criteria based on pattern analysis (pigment network, blue-gray areas, vascular pattern) and tumor thickness. This technique could be useful in the preoperative assessment of tumor thickness as an indication for sentinel node biopsy. Objective: Our purpose was to evaluate the possible role of the total dermatoscopy score (TDS) assigned to a series of lesions in accordance with the ABCD rule of dermatoscopy as a preoperative predictor of melanoma thickness. Methods: For 84 cutaneous melanomas (17 were in situ melanomas; 67 invasive cases with mean thickness 0.93 mm; range, 0.2–3.9 mm; standard deviation, 0.63) consecutively excised at the Department of Dermatology of Florence, TDS was established by two observers blinded as to the tumor thickness. The performance of different cut-off points of TDS in the diagnosis of melanoma with Breslow's thickness more than 0.75 or 1.00 mm was investigated by receiver operating characteristic (ROC) analysis. Accuracy of classification was evaluated in terms of sensitivity, specificity, and area under ROC curves (AUC). Results: The TDS assigned to cutaneous melanomas by the ABCD rule increased with the thickness of the lesions from in situ melanomas to melanomas of intermediate thickness (0.75–1.50 mm). As a preoperative method for the detection of melanomas with a Breslow thickness greater than 0.75 mm, a TDS cut-off point of 6.80 showed 80% sensitivity, 84% specificity, and 82% diagnostic accuracy (AUC value, 0.90). TDS performed better in the diagnosis of a thickness threshold of 0.75 than 1.00 mm (higher AUC value). Conclusion: The TDS calculated by the ABCD rule of dermatoscopy-a simplified approach to dermatoscopic diagnosis of melanoma-provides useful information for the preoperative assessment of melanoma thickness greater than 0.75 mm. (J Am Acad Dermatol 2000;43:459–66.)