In a controlled clinical trial based on 30 geriatric patients with recurrent urinary tract infection, 12 out of 17 patients fulfilled a 12-month treatment with sulphamethoxazole/trimethoprim (Bactrim®) with continuous sterile urine compared to 1 out of 13 patients treated with nitrofurantoin (p < 0.05). There was a slight but statistically significant increase in serum creatinine during treatment for 12 months in the sulphamethoxazole/trimethoprim group, but this probably does not reflect any deterioration in kidney function. The remaining laboratory values showed no significant changes whatsoever