Psoriatic arthritis (PA) is a chronic systemic disease that is difficult to detect. The diagnosis is made on mainly clinical grounds based on the findings of psoriasis and inflammatory arthritis of the joints. Many reports have described the damaging effects of PA on the temporomandibular joints (TMJs), but no study has clearly reported the TMJ as the first articulation to be involved in PA. This article reports a case of PA that was diagnosed several years after TMD onset because no signs besides psoriasis were present. The missed early diagnosis resulted in severe TMJ damage. The TMJ can be the first joint involved in PA. For a correct, early diagnosis of PA, collaboration between dental clinicians and rheumatologists is very important.