The aim of this study was to determine the etiologic agents associated with community-acquired pneumonia in 104 French children ages 18 months to 13 years. Potential respiratory pathogens were identified in 87 (85%) cases; these included respiratory syncytial virus in ten, other viruses in 20, Streptococcus pneumoniae in 14 and Mycoplasma pneumoniae (diagnosed by serologic procedures) in 43. Of 32 patients with Mycoplasma pneumoniae infection who were initially treated with beta-lactam antibiotics, 30 failed treatment. Recovery from mycoplasma infection occurred rapidly in patients treated with macrolide antibiotics (which included spiramycin in 31 patients, josamycin in 7, and erythromycin in 3); however, cough persisted in 12 patients for one month. The high frequency of Mycoplasma pneumoniae in children over 18 months of age must be considered when selecting an antibiotic for initial therapy.