It is not easy to predict the clinical course of longitudinal melanonychia (LM) in children because few prospective studies have been conducted. In our prospective study 15 Japanese children with LM were followed for more than 2 years. Eight patients demonstrated gradual fading of LM. Clinical features such as the patient's sex and the site, age of onset, duration, color, and width of the melanonychia were not significantly associated with the outcome. Dots distributed along melanotic lines, a finding we referred to as dots and lines, can be a dermoscopic sign of regression of melanonychia in children with LM. In this study, the presence of dermoscopically observed dots was significantly related with regression of melanonychia (P = .019; odds ratio, 18.0).