There has been a dramatic increase in the incidence of malignant melanoma in most parts of the world. Because the tumor thickness is the most important prognostic factor for the prognosis of the malignant melanoma, the early detection of thin melanomas is essential. Dermatoscopy allows the physician to discriminate between melanocytic and nonmelanocytic lesions with high diagnostic accuracy and to detect initial malignant melanomas. We review the principles of dermatoscopy and the differential diagnosis of pigmented skin lesions. Before using the ABCD rule of dermatoscopy to classify melanocytic lesions into benign, suspicious, or malignant, the distinction between melanocytic and nonmelanocytic lesions is necessary. An essential prerequisite for the usefulness of this technique is adequate training.