Sulfasalazine is an antirheumatic drug used in the treatment of AS and rarely causes serious psychiatric problems such as mania, depression and psychosis. This present case reports a male patient who presented due to major depressive disorder with psychotic features. He had been receiving 1000 mg/day sulfasalazine for AS while he developed serious psychiatric symptoms. The patient was stopped being given sulfasalazine after consulting rheumatology, as it was suspected sulfasalazine might have been the cause of his psychiatric symptoms. Complaints were fully resolved 4 months after the beginning of the 1 year psychiatric treatment. When the cases in the literature are taken into account, it is necessary to be aware of the possible psychiatric side effects of sulfasalazine