NAMCS is a national probability sample survey of visits to nonfederal, office-based physicians conducted annually by CDC. NAMCS samples visits during randomly assigned 1-week reporting periods throughout the year and collects patient demographic information, diagnostic codes for up to three diagnoses, and prescription information from the medical record. Diagnoses of the five ARIs, most episodes of which do not require antibiotic treatment, were identified using the following International Classification of Diseases, Ninth Revision, Clinical Modification codes for the primary diagnosis: 381.0, 381.4, 382.0, 382.4, 382.9 (otitis media); 466.0, 490 (bronchitis); 462, 463 (pharyngitis); 461, 473 (sinusitis); and 460, 465 (nonspecific upper respiratory infection [common cold]). Details of NAMCS methodology have been described previously.* To quantify and assess antibiotic prescribing practices, the first five drug prescriptions recorded for each visit were examined, and the number of antibiotic prescriptions counted. Data were weighted to produce national estimates, and combined in 2-year periods to improve the reliability of estimates.