Background: Epiluminescence microscopy (ELM) provides for increased accuracy in the clinical diagnosis of pigmented skin lesions (PSL). It is based on pattern analysis of ELM criteria, which requires experience. The recently introduced application of the ABCD score to ELM facilitates this by permitting lesion evaluation on the basis of predefined clinical criteria. Objective: The present study was performed to evaluate the diagnostic performance of the ABCD rule for ELM in pigmented skin lesions testing dermatologists with varying skills from novice to expert. Methods: Two hundred fifty electronic images of randomly selected, histologically proven PSL including 41 early melanomas (16.4%) were presented to the raters, and each image was scored according to the rules of the ABCD score and rated without the guidance of a scoring system on a scale from 1 = definitely benign to 5 = definitely melanoma. Results: Our data show that the application of the ABCD rule significantly enhances diagnostic ability in less experienced dermatologists compared with rating without the guidance of a scoring system. In contrast, the diagnostic accuracy of dermatologists who are moderately to greatly experienced is not improved by use of the ABCD rule. Conclusion: Our experiments indicate that the application of the ABCD rule to ELM introduced by Stolz et al represents a useful enhancement for diagnosis of pigmented skin lesions in less experienced users. However, the method does fail to detect melanomas with 100% accuracy. Therefore further effort has to be made to make the diagnosis of melanoma easier and more accurate. (J Am Acad Dermatol 1999;40:171-6.)