Nail involvement is a common feature in psoriasis as 10-78% of psoriasis patients are affected and the percentage increases up to 85% in psoriatic patients. However, isolated nail psoriasis without cutaneous lesion constitutes only 5-10% of the patients. It is difficult to differentiate isolated nail psoriasis with other nail disease, such as, onychomycosis. They can even coexist and make it difficult to treat. As nail psoriasis can be a first manifestation of psoriatic arthritis or prognostic factor of psoriatic arthritis, early recognition and treatment of nail psoriasis in important. Herein, we report the difficult case of 67-year-old woman who were first treated as twenty nail dystrophy by onychomycosis but turned out to be nail psoriasis with onychomycosis after the diagnosis of psoriatic arthritis after 2 years later.