In this multicenter, investigator-blind trial, we compared the efficacy and safety of azithromycin and cefadroxil for the treatment of uncomplicated skin and skin structure infections (SSSIs). A total of 296 patients were randomized to receive either azithromycin (500 mg on day 1, followed by 250 mg once a day on days 2 to 5) or cefadroxil (500 mg twice a day for 10 days). Outpatients, ranging in age from 18 to 75 years, with acute uncomplicated SSSIs were enrolled in the study. Clinical and bacteriologic response was assessed between days 10 and 13 (primary end point) and between days 28 and 32. In a modified intent-to-treat analysis, clinical success rates assessed between days 10 and 13 were 97% (111/114) for azithromycin and 96% (101/105) for cefadroxil (P=.717). For azithromycin and cefadroxil, corresponding rates of bacteriologic eradication for Staphylococcus aureus were 94% (64/68) and 86% (60/70), respectively, and for Streptococcus pyogenes, 80% (4/5) and 100% (6/6), respectively. Clinical success rates assessed between days 28 and 32 were 100% (82/82) for azithromycin compared with 90% (75/83) for cefadroxil (P=.007). Corresponding rates of eradication for S aureus were 100% (59/59) versus 89% (56/63), respectively; and for S pyogenes, 100% (4/4) versus 83% (5/6), respectively. The incidence of treatment-related adverse events was similar in the 2 treatment groups. However, 5 of the 139 patients (4%) in the cefadroxil group discontinued therapy because of treatment-related adverse events compared with none of the 152 patients in the azithromycin group (P=.02). Five-day therapy with azithromycin was as effective as 10-day therapy with cefadroxil for treating uncomplicated SSSIs.