Bladder dysfunction occurs at some time in most patients with multiple sclerosis and these patients are prone to have recurrent urinary tract infections. Cranberry has been traditionally used for the treatment and prophylaxis of urinary tract infections but there is no reliable randomized controlled trial demonstrating evidence of cranberry's utility in this disease. The aim of our study is to assess the efficacy and safety of cranberry in the prophylaxis of urinary tract infections in patients with multiple sclerosis with a prospective randomized, double-blind and placebo-controlled clinical trial.