The impact of a health education program to help families manage chronic disease will be determined not only by the demonstrated effectiveness of the intervention but also by the quality and breadth of program implementation. A theory-based intervention is evaluated that diffuses the Cystic Fibrosis Family Education Program (CF FEP) to approximately 20,000 families nationwide. Surveys of 106 Cystic Fibrosis Foundation-certified CF centers are used in a cross-sectional study of the theory-based determinants of diffusion. Results describe: (1) the proportion of CF centers targeted who adopted and implemented the CF FEP; (2) the perceptions of program or center characteristics associated with program use, fidelity and maintenance/institutionalization; and (3) the relationship between the method of decision-making used by the center to adopt the program and program use, fidelity, and maintenance/institutionalization.