The authors used an actual-work estimate method to estimate the cost of developing a tailored interactive computer education program to improve compliance with colorectal cancer screening guidelines in a large multi-specialty group medical practice. Resource use was prospectively collected from time logs, administrative records, and a design and computing subcontract. Sensitivity analysis was performed to examine the uncertainty of the overhead cost rate and other parameters. The cost of developing the system was Dollars 328,866. The development cost was Dollars 52.79 per patient when amortized over a 7-year period with a cohort of 1,000 persons. About 20% of the cost was incurred in defining the theoretic framework and supporting literature, constructing the variables and survey, and conducting focus groups. About 41% of the cost was for developing the messages, algorithms, and constructing program elements, and the remaining cost was to create and test the computer education program. About 69% of the cost was attributable to personnel expenses. Development cost is rarely estimated but is important for feasibility studies and ex-ante economic evaluations of alternative interventions. The findings from this study may aid decision makers in planning, assessing, budgeting, and pricing development of tailored interactive computer-based interventions.