Although some "how-to" guides have been written on tailored messaging, we found no reports on lessons learned from the process of developing a tailored intervention. Such lessons may be useful for practitioners and researchers who are new to tailored intervention development. The authors describe lessons gleaned from the process of developing a repeat mammography tailored print intervention. Lessons learned include the following: Selection of determinants appropriate for tailoring should be based on a theoretic framework and refined through assessment of the target population; researchers should anticipate threats to fidelity of intervention delivery because of incomplete or illogical survey data; fingerprinting enables assessment of intervention dose and how it relates to effectiveness of the tailored intervention; and a systematic process for conducting a systems test is needed to check for inconsistencies and errors before final tailored letter production. These lessons are discussed in the context of challenges and possible solutions for tailored health communication.