In a medical screening program for early detection of disease 1 or more screening modes are administered to an apparently healthy population. Knowledge of the true disease status for all screened individuals would allow estimation of the false negative and false positive rates for each mode of detection and for the program as a whole. This paper develops capture-recapture methods applicable to programs when follow-up of individuals negative on screening is not performed or is incomplete. The methods require at least 2 independent modes of detection. Data from a breast cancer screening program illustrate the procedures. The results of 4 screening examinations at approximately 1 yr intervals and the long-term follow-up of all screened individuals support the usefulness of these methods in the evaluation of a screening program.