Trichomonosis, the disease caused by the protozoan parasite Trichomonas vaginalis, is the most common curable sexually transmitted disease with 174 million cases per year worldwide. The emerging resistance against the current standard therapy with metronidazole is pushing the search for alternative drugs. The purpose of this study was to determine the efficacy of curcumin, a derivate of Curcuma longa, on T. vaginalis. The effective concentrations (ECs) were evaluated using three strains of T. vaginaliswith different metronidazole susceptibilities (ATCC 30001, ATCC 30236 and ATCC 50138) and dilution series of curcumin in 24-well microtitre assays. Curcumin was shown to be highly effective against T. vaginalis, and the susceptibility of the different strains was not affected by an existing resistance to metronidazole. After 24 h of incubation, the EC50 ranged from 73.0 to 105.8 µg/ml and the EC90 from 216.3 to 164.9 µg/ml. In all strains tested, a 100 % eradication of all trichomonal cells within 24 h was reached at a concentration of 400 µg/ml curcumin, the 50-fold concentration still being very well tolerated by human mucosa. Altogether, curcumin seems to be a promising candidate for topical treatment of trichomonosis.