Psoriasis is a recurrent chronic inflammatory skin disease with various mild to severe clinical manifestations. The relationship between severity of the skin lesions and nail involvement has always been underestimated.Aim of the study was to evaluate the severity of skin involvement in psoriatic patients with and without nail manifestations.In this analytic cross-sectional study, patients with psoriasis referred to Razi University Hospital of Rasht from November 2015 to March 2016 were enrolled. Demographical features (i.e. age, gender) were obtained. Psoriasis severity and nail involvement criteria were assessed by Psoriasis Area and Severity Index (PASI) and Nail Psoriasis Severity Index (NAPSI), respectively. All the gathered data were analyzed by SPSS software.In this study, 71 psoriatic patients with a mean age of 39.23±17.9 years (mean ± Standard Deviation; range: 4 to 77 years old) were studied. 22 patients (31%) had nail involvements. PASI scores were 11.7±5.7 and 5.7±4.5 in the two groups with and without nail involvements, respectively (P<0.001). There were no significant differences between age, age of onset, and duration of the disease between the two groups (P>0.05).The correlation coefficient between PASI and NAPSI was 0.367, which was statistically significant (P<0.001).Based on the findings of our study, nail involvement is an important criterion in determining the severity of skin manifestations in psoriatic patients. Additionally, a high percentage of such patients probably manifest both skin and nail manifestations. Therefore it is highly recommended to consider nail involvement when evaluating psoriasis. </p
