Objective: To determine the utility of the current diameter criterion of larger than 6 mm of the ABCDE acronym for the early diagnosis of cutaneous melanoma. Design: Cohort study. Setting: Dermatology hospital-based clinics and community practice offices. Patients: A total of 1323 patients undergoing skin biopsies of 1657 pigmented lesions suggestive of melanoma. Main Outcome Measure: The maximum lesion dimension (diameter) of each skin lesion was calculated before biopsy using a novel computerized skin imaging system. Results: Of 1657 biopsied lesions, 853 (51.5%) were 6 mm or smaller in diameter. Invasive melanomas were diagnosed in 13 of 853 lesions (1.5%) that were 6 mm or smaller in diameter and in 41 of 804 lesions (5.1%) that were larger than 6 mm in diameter. In situ melanomas were diagnosed in 22 of 853 lesions (2.6%) that were 6 mm or smaller in diameter and in 62 of 804 lesions (7.7%) that were larger than 6 mm in diameter. Conclusion: The diameter guideline of larger than 6mm provides a useful parameter for physicians and should continue to be used in combination with the A, B, C, and E criteria previously established in the selection of atypical lesions for skin biopsy.