Abstract Purpose Interstitial cystitis is a debilitating bladder disease of unknown etiology with no cure. A recent report suggested that bacillus Calmette-Guerin (BCG) may be effective in the treatment of interstitial cystitis. A randomized, prospective, double-blind, placebo controlled trial to evaluate the safety and efficacy of intravesical BCG in treating interstitial cystitis was done. Materials and Methods Patients meeting the National Institute of Arthritis, Diabetes and Digestive and Kidney Diseases criteria for interstitial cystitis received 6 weekly instillations of Tice strain BCG or placebo. Periodic questionnaires, voiding diaries and cystometrograms were obtained. A total of 30 evaluable subjects was enrolled in the study with a mean followup of 8 months (range 6 to 13). Based on an exit questionnaire a responder was defined as one who rated the interstitial cystitis symptoms as moderately improved or better. Results A 60% BCG response rate was noted, compared to a 27% placebo response rate. Minimum voided volume and quality of life improved in the BCG group compared to placebo. Adverse events were similar in each group, mostly irritative in nature, and no significant systemic events were noted. Conclusions Intravesical Tice strain BCG appears to be safe and efficacious in the treatment of interstitial cystitis. Additional studies must be performed to confirm the results of this pilot study.