Sinfrontal, a complex homeopathic medication, is popular in Germany for the treatment of ear, nose and throat and respiratory tract infections. Unlike many other homeopathic or herbal medications, the efficacy and safety of Sinfrontal has been demonstrated in a number of clinical studies of patients with sinusitis. To assess the cost effectiveness of Sinfrontal versus placebo in the treatment of adults with acute maxillary sinusitis (AMS) in Germany. A secondary objective was to assess the cost effectiveness of Sinfrontal versus standard treatment with antibacterials. Sinfrontal was compared with placebo in a cost-utility analysis based on data from a randomized controlled clinical trial over 3 weeks (Sinfrontal group: n = 57; placebo group: n = 56). Trial data were analysed from a societal perspective; resource use was valued with German unit costs for 2005. In a secondary analysis, the longer-term cost utility of Sinfrontal versus placebo was estimated over a total of 11 weeks based on an 8-week post-treatment observational phase. In addition, the cost effectiveness of Sinfrontal versus antibacterials was determined based on an indirect comparison of placebo-controlled trials. Sinfrontal led to incremental savings of euro 275 (95% CI 433, 103) per patient compared with placebo over 22 days, essentially due to the markedly reduced absenteeism from work (7.83 vs 12.9 workdays). Incremental utility amounted to 0.0087 QALYs (95% CI 0.0052, 0.0123), or 3.2 quality-adjusted life-days (QALDs). Bootstrapping showed that these findings were significant, with Sinfrontal being dominant in 99.9% of simulations. The results were robust to a number of sensitivity analyses. In the secondary analysis, Sinfrontal led to incremental cost savings of euro 511 and utility gains of 0.015 QALYs or 5.4 QALDs compared with placebo. Compared with antibacterials, Sinfrontal had a significantly higher cure rate (11% vs 59%; p < 0.001) at similar or lower costs. The results of this economic evaluation indicate that Sinfrontal may be a cost-effective treatment for AMS in adults.