A double-blind, double-dummy trial comparing a single dose treatment with fosfomycin trometamol (FT, 3 g) versus trimethoprim (TMP, 200 mg) was carried out in women with uncomplicated urinary tract infections. From 51 clinically evaluable patients, 44 were bacteriologically assessable at the 6-week follow-up. The results were as follows in the FT group (n = 22): eradication in 17 (77.3%); recurrence in 2 (9%); reinfection in 2 (9%), and persistence in 1 (4.5%). For the TMP group (n = 22) the results were: eradication in 12 (54.5%); recurrence in 1 (4.5%); reinfection in 1 (4.5%), and persistence in 8 (33.3%). There were no significant adverse events reported with either agent.