The authors report a case of community-acquired pneumonia in a patient with chronic obstructive lung disease. The initial antibiotic therapy consisted of an amoxicillin-clavulanic acid combination and intravenous macrolides. Twenty-four hours after admission, blood cultures were positive for pneumococcus. Pending the results of disc sensitivity tests, the antibiotic therapy was modified and amoxicillin alone was prescribed. Clinical deterioration then developed rapidly, as the pathogen was amoxicillin-resistant. Subsequently, the patient recovered under erythromycin therapy. As illustrated by this case, the emergence of pneumococci resistant, or showing low sensitivity to penicillins raises the problem of the antibiotic therapy to be used against community-acquired lung diseases.