Pigmented and nonpigmented nail abnormalities often represent a challenge for clinicians because many, and sometimes potentially life-threatening differential diagnoses must be taken into consideration. Although many details of nail diseases can already be assessed with the naked eye, dermoscopy opens up a second microscopic level of inspection, which can be very useful for the diagnostic process. In the last 20 years dermoscopy has made rapid progress in the further development of criteria for the early recognition of melanoma. In addition, the use of dermoscopy has been extended to the examination of cutaneous adnexa, such as hairs (trichoscopy) and nails (onychoscopy). Many, sometimes highly specific criteria for the dermoscopic assessment of nail diseases have been described in a series of recently published articles. This review article provides important diagnostic aids for a well-founded dermoscopic assessment of nail diseases.