Cranberry cocktail has been reported to reduce bacteriuria and pyuria in elderly women and self-reported urinary tract infection (UTI) in young female undergraduates, but commercially prepared cranberry concentrate supplements have never been evaluated in multiple sclerosis (MS) patients with neurogenic bladder. The purpose of this study was to determine whether one 8,000-mg cranberry concentrate supplement daily could prevent UTI in MS participants with bladder symptoms. We conducted a double-blind, randomized, placebo-controlled longitudinal trial of cranberry supplement versus placebo with participants who have MS. After informed consent had been obtained from the participants, baseline data were collected and participants were randomized to receive either one cranberry supplement or placebo daily for 6 months. The sample consisted of 135 participants. In the cranberry group 34.6% of participants failed (i.e., developed a UTI) versus 32.4% in the control group (p = .849). Not all cranberry supplements have been found to contain proanthocyanidins, the active ingredient of cranberries. Because there is no way for the consumer to distinguish supplements that contain proanthocyanidins from those that do not, taking juice or whole cranberries may be preferrable.