Illness presentation in the elderly may be entirely non-specific, with fatigue, loss of function or the presence of geriatric syndromes. We report a 90 years old male consulting in the emergency room for delirium that persisted throughout hospitalization without finding a cause. During the course of hospitalization mild fever appeared and a left knee swelling became apparent. A synovial fluid aspiration showed a leukocyte count of 360 per field with 60% polymorphonuclear cells. The culture was negative. With a presumptive diagnosis of pseudogout, cochicine and celecoxib were started with remission of the confusional state. The patient was discharged 13 days after admission in good conditions.Illness presentation in the elderly may be entirely non-specific, with fatigue, loss of function or the presence of geriatric syndromes. We report a 90 years old male consulting in the emergency room for delirium that persisted throughout hospitalization without finding a cause. During the course of hospitalization mild fever appeared and a left knee swelling became apparent. A synovial fluid aspiration showed a leukocyte count of 360 per field with 60% polymorphonuclear cells. The culture was negative. With a presumptive diagnosis of pseudogout, cochicine and celecoxib were started with remission of the confusional state. The patient was discharged 13 days after admission in good conditions.