Background / Objectives:Dermoscopy is a non-invasive technique that has been recognized recently as an effective tool in the diagnosis of nail diseases, including nail psoriasis. The aim of this study was to clarify specific dermoscopic features of nail psoriasis and identify those that are correlated with disease severity. Methods: We conducted a prospective study over 18 months. Fifty patients followed for psoriasis and nail involvement were enrolled. Following a clinical examination, the patients were classified according to the Nail Psoriasis Severity Index (NAPSI) and the Psoriasis Area and Severity Index (PASI). A dermoscopic examination of all fingernails was performed, including the nail plate, periungual folds, subungual area, cuticule and hyponychium. Results: The most frequently observed dermoscopic features were distal onycholysis (90%), subungual hyperkeratosis (80%), splinter haemorrhage (72%), paronychia and mottled lunula (62%), followed by dilated capillaries in the hyponychium (50%), pitting (48%), trachyonychia (42%), erythematous border of an onycholytic area (40%) and leukonychia (32%). Statistically significant relationships were observed between the severity of psoriasis, as determined using PASI, and the presence of pachyonychia, pitting, distal onycholysis, paronychia, onychomadesis as well as the presence of red lunula, mottled lunula, dilated capillaries of the hyponychium and crumbling. As well, pachyonychia, paronychia, splinter haemorrhage, onychomadesis, mottled lunula, trachyonychia and crumbling were relevant to nail psoriasis severity. Conclusions:Dermoscopy can improve the accuracy of nail psoriasis diagnostic. We have demonstrated positive associations between a number of dermoscopic manifestations and disease severity.