Background Twenty-nail dystrophy (TND) is an idiopathic and non-congenital nail dystrophy that is characterized by excess longitudinal ridges and loss of luster in multiple nail plates. There are a few studies on TND. Materials and methods In order to investigate the demographic and clinical characteristics of patients with TND in Korea, a retrospective study was performed. Eighty-eight patients were diagnosed with TND from February 1, 2003, to April 30, 2010. Results In this study, morphology of TND was clinically divided as atrophic, hypertrophic, pitting dominant, shallow fissure-dominant, and deep fissure-dominant types. The patients consisted of 33 males and 55 females. The proportions of subtype and gender predominance showed differences between the childadolescent-onset TND (20 cases) and the adult-onset TND (68 cases). Conclusion The clinical data of this study contribute to our understanding of TND.