While clinical trials of medications often use a double-blind procedure, the integrity of the blind and its relationship to treatment outcome is seldom examined. In this review, 73 double-blind, placebo-controlled clinical trials of the nicotine replacement therapies (NRTs) in smoking cessation were identified. Seventeen articles were found that assessed blindness integrity, demonstrating major variations in the assessment, analysis, and reporting of blindness integrity. Although 12 studies found that subjects accurately judged treatment assignment at a rate significantly above chance, the available literature does not permit definitive conclusions about blindness integrity. Recommendations for the assessment, analysis, and reporting of blindness integrity are made.