This multicenter, randomized, double-blind trial compared the efficacy and safety of ciprofloxacin (CIP; 500 mg twice daily for 10 days, placebo for 4 days) to those of clarithromycin (CLARI; 500 mg twice daily for 14 days) in 560 adults with clinically documented and radiologically confirmed acute sinusitis. Of 457 efficacy-valid adults (236 CIP, 221 CLARI), clinical resolution plus improvement at the end of therapy was 84% for CIP-treated patients compared to 91% of CLARI recipients (CI95 = -0.131, -0.013). At the 1-month follow-up, more than twice as many CLARI-treated patients, 18 (10%), experienced a relapse, compared to 7 (4%) CIP-treated patients. The combined clinical response analyses (end of therapy and 1 -month follow-up) demonstrated that CIP and CLARI were statistically equivalent (CI95 = -0.106, 0.044). Diarrhea, nausea, headache, and dizziness were the most frequently reported drug-related adverse events in both treatment groups; diarrhea and taste perversion were reported more frequently among CLARI recipients. In summary, the combined end of therapy and follow-up clinical evaluation analyses revealed that CIP and CLARI were equally effective in the management of acute sinusitis, although twice as many relapses were reported among CLARI recipients.