Computerized adaptive testing (CAT) and Item Response Theory (IRT) techniques were applied to the Schedule for Nonadaptive and Adaptive Personality (SNAP) to create a more efficient measure with little or no cost to test reliability or validity. The SNAP includes 15 factor analytically derived and relatively unidimensional traits relevant to personality disorder. IRT item parameters were calibrated on item responses from a sample of 3,995 participants who completed the traditional paper-and-pencil (P&P) SNAP in a variety of university, community, and patient settings. Computerized simulations were conducted to test various adaptive testing algorithms, and the results informed the construction of the CAT version of the SNAP (SNAP-CAT). A validation study of the SNAP-CAT was conducted on a sample of 413 undergraduates who completed the SNAP twice, separated by one week. Participants were randomly assigned to one of four groups who completed (1) a modified P&P version of the SNAP (SNAP-PP) twice (n = 106), (2) the SNAP-PP first and the SNAP-CAT second (n = 105), (3) the SNAP-CAT first and the SNAP-PP second (n = 102), and (4) the SNAP-CAT twice (n = 100). Results indicated that the SNAP-CAT was 58% and 60% faster than the traditional P&P version, at Times 1 and 2, respectively, and mean item savings across scales were 36% and 37%, respectively. These savings came with minimal cost to reliability or validity, and the two test forms were largely equivalent. Descriptive statistics, rank-ordering of scores, internal factor structure, and convergent/discriminant validity were highly comparable across testing modes and methods of scoring, and very few differences between forms replicated across testing sessions. In addition, participants overwhelmingly preferred the computerized version to the P&P version. However, several specific problems were identified for the Self-harm and Propriety scales of the SNAP-CAT that appeared to be broadly related to IRT calibration difficulties. Reasons for these anomalous findings are discussed, and follow-up studies are suggested. Despite these specific problems, the SNAP-CAT appears to be a viable alternative to the traditional P&P SNAP. (PsycINFO Database Record (c) 2003 APA, all rights reserved).