Objective: The lack of consistency between peoples' attitudes toward organ donation and organ donation registration behavior has long perplexed scholars. Ajzen and Fishbein's principle of compatibility offers a potential explanation for the attitude-behavior discrepancy. This principle states that attitudes will better predict behavior if the specificity of a measured attitude matches the specificity of the behavior under consideration. Method: Two studies, using different samples and different modes of data collection, measured general attitudes toward organ donation and specific attitudes toward registering as a donor, while simultaneously offering a registration opportunity. Results: Compared with general attitudes about organ donation, attitudes specific to organ donor registration were superior predictors of registration intentions and behaviors. Specific attitudes explained at least 70% more variance in registration behaviors than general attitudes. Conclusion: The lack of attitude-behavior consistency in the organ donor domain can be partially explained by limited compliance with the principle of compatibility.