We report a case of a 61-years-old woman in remission of psoriasis for 20 years. She presented recurrence of psoriasis in the form of plaques few days after taking L-methylfolate 15mg/day. The L-methylfolate was prescribed as an adjuvant for the treatment of depression in a patient with the methylenetetrahydrofolate reductase gene polymorphism (MTHFR).