Objective To investigate the clinical manifestations, diagnosis, treatment and prognosis of psittacosis patients. Methods The clinical features, treatment and prognosis of severe pneumonia caused by Chlamydia psittaci were analyzed and relevant literatures were reviewed. Results An 83-year-old male with a history of type 2 diabetes mellitus was admitted to the hospital for "fever, cough for 5 days and dyspnea for 3 days". Chest CT showed a large mass of increased density in the right lung; CD4+ T lymphocytes had an absolute value of 23 cells/μL; Blood gas analysis showed type Ⅰ respiratory failure; Chlamydia psittaci was detected by metagenomic next-generation sequencing. The patient was diagnosed of severe pneumonia (Chlamydia psittaci), type 2 diabetes mellitus, suspected central nervous system infection. This patient was treated with doxycycline and macrolides antibiotics and discharged from hospital after complete recovery. Literature review showed that patients got infected from contacting sick bird, manifested with multiple system involvement. Respiratory symptoms were common, while central nervous system infection seemed to be rare. The diagnosis of psittacosis depended on serology, nucleic acid detection, pathogen isolation and culture. Metagenomic next-generation sequencing had superiority in the diagnosis of psittacosis. Tetracyclines were the preferable treatment, such as doxycycline or tetracycline, with a duration of at least 10 to 14 days. The prognosis of psittacosis was well, and most of the severe and even life-threatening cases were caused by unclear diagnosis and delayed treatment, and the overall mortality rate was about 1%. Conclusions Psittacosis is one kind of zoonoses. History of poultry exposure is helpful in diagnosis, and metagenomic next-generation sequencing has advantages in diagnosing psittacosis. Tetracyclines are preferred with adequate course of treatment. The overall prognosis is good.