In a prospective randomized study 38 patients with recurrent urinary tract infections (rUTI) were included to take either 50 mg Nitrofurantoin (n = 19) or 50 mg Trimethoprim (n = 19) as low-dose long-term prophylaxis for half a year. Compliance was checked weekly by Bacillus subtilis spore test strips sent in by mail. The infection rate was reduced from more than three per patient year to 0.01. There were no significant differences between the two groups concerning the recurrence rate (Nitrofurantoin: one rUTI; Trimethoprim: three rUTI) or side effects. Under Nitrofurantoin treatment 3 symptomatic fungal infections occurred. Trimethoprim and Nitrofurantoin are equally suitable for low-dose long-term prophylaxis in rUTI. Surveillance of compliance gives important hints for failure of prophylaxis.