Introduction: Various skin diseases such as psoriasis, lichen planus, and alopecia areata can be associated with structural nail lesions. However nail lesions prevalence in patients with severe acne vulgaris is not determined. This study aimed to determine the frequency and types of nail lesions in patients with severe acne vulgaris.Methods: In this cross-sectional study, 235 patients with severe acne vulgaris were included from the clinic of dermatology of RasoulAkram Hospital during the years 2010 and 2011. The patients had no history of treatment for acne vulgaris. Patients initially underwent clinical examination, and severity of acne was determined among them. Demographic characteristics such as gender, age, and blood type, and Nail disorders including brittleness, Onycholysis, and Leukonychia were investigated in these patients. Data were analyzed using SPSS 18 software.Results:In this study79 patients with severe acne vulgaris (33.6%) had nail involvement and the frequency of nail lesions in this study was as follows: brittle nails 26.8% (63 cases); Leukonychia 18.2% (43 cases); Parrot beaked nails 3.4% (8 cases) and Onycholysis 1.3% (3 cases). Nail disorders in patients with severe acne vulgaris was not associated with sex, blood group, and the severity and distribution of acne lesions. But the lower age of the patients was associated with the incidence of nail disorders.Conclusion: According to high prevalence of nail involvement, especially brittle nails in patients with severe acne vulgaris, investigation and treatment of nail disorders in these patients have a great importance.