Multilog (Thissen, 1991) was used to estimate parameters of 225 items from the Quebec Adaptive Behavior Scale (QABS). A database containing actual data from 2,439 subjects was used for the parameterization procedures. The two-parameter-logistic model was used in estimating item parameters and in the testing strategy. MicroCAT (Assessment Systems Corporation, 1989) was then used to manage the item banks and Computerized Adaptive Testing (CAT) environment during a simulation run using data from a randomly selected sample of 200 subjects taken from the larger data base. The simulation of the QABS-CAT testing indicates that levels of ability can be estimated for each of the seven skill domains by using only 30% of the items of the conventional version. The numerous advantages of item response theory and CAT as applied to the assessment of adaptive behavior with regard to the changing definition of mental retardation (Luckasson et al., 1992) are discussed. (Author/SLD)