A previously well 56 year-old woman presented with an adult respiratory distress syndrome which worsened under penicillin treatment, responding only to erythromycin and rifampicin, as well as CPAP ventilation. Diagnostic serology was positive to Chlamydia psittaci. Psittacosis is not a frequent cause of primary extensive pneumonia in intensive care units; other diseases should be looked for in the presence of these non-specific clinical and biological pictures (Legionella pneumophila, Mycoplasma pneumoniae, Streptococcus pneumoniae). Pneumocystis should also be looked for in a typical pneumonia; erythromycin is the antibiotic of first choice in the treatment of primary extensive pneumonia.