The aim of the province-wide Ontario Breast Screening Program (OBSP) is to reduce breast cancer mortality through providing screening for breast cancer to all Ontario women 50 and over. The authors identify the components of the OBSP and the organizational, political, and financial challenges and biases affecting its evaluation. They then argue that because key players have not yet established program goals from which process and outcome indicators can be identified, a goal-directed evaluation is not currently possible. They therefore develop a framework to permit the identification, categorization, and prioritization of all factors that need to be addressed in a comprehensive evaluation of the OBSP. This evaluation approach may be of assistance to evaluators of other complex programs about which consensus on program goals has not yet been attained.