We analyzed data from the WASI-II manual to determine discrepancy score reliabilities of the Verbal Comprehension (VCI) and Perceptual Reasoning (PRI) indexes and the four subtests in the child and adult standardization samples. Reliabilities of the VCI-PRI discrepancy scores range from 0.78 to 0.86 for children and 0.82 to 0.89 for adults and generally are large enough to justify hypothesis generation. Discrepancy score reliabilities of the subtests range from 0.64 to 0.82 and 0.66 to 0.84 for children and adults, respectively, and therefore must be considered on a score-by-score basis in formulating hypotheses. Tables are provided to identify significant differences between pairs of subtests and to determine ipsative strengths and weaknesses when each subtest is compared to the mean of four subtests. The use of confidence intervals for the interpretation of discrepancy scores is presented. If additional discrepancy score reliabilities and cut-offs are desired, the necessary formulas are provided.