Adult Still's disease is a rare systemic inflammatory disorder of unknown etiology predominantly affecting women with a heterogeneous clinical presentation.

Typical features include high fever, arhtralgia and an evanescent rash and less frequently lymphadenopathy, hepatosplenomegaly, leukocytosis, anemia, pleuritis, and pericarditis the involvement of central nervous system is rare. Diagnosis is made by exclusion and strictly based upon clinical criteria, with differential diagnosis including infection, malignancy, and immunologic disorders. the clinical spectrum of the disease is variable and initial therapy of choice is high doses of non-steroidal anti-inflammatory drugs. Prognosis is reserved; with frequent exacerbations over the course of the disease.

We describe a case of 69 years old man, with past medical history of prostate cancer, arterial hypertension and dyslipidemia, admitted in emergency service with persistent fever, asthenia e anorexia. No previous psychiatric history was reported. During the first days of hospitalization, a cutaneous rash on lower limbs was apparent together with increased levels of blood inflammatory markers. A change in behavior was observed, with psychomotor agitation, persecutory and grandiosity delusions. After a detailed clinical and laboratory investigation Adult Still's disease was diagnosed.

With introduction of corticoid therapy the patient gradually improved - there was a significant reduction of systemic inflammation as well as an improvement of psychotic symptoms.

The case presented illustrates a psychiatric manifestation not yet reported in this medical condition.