Relationships, including age, race, gender, and IQ level, between the Wechsler intelligence scales (WISC-R, WAIS-R) and the Peabody Picture Vocabulary Test-Revised (PPVT-R) were studied among 206 applicants for disability benefits in a private practice setting. We found that the PPVT-R seriously underestimated WISC-R IQs by an average of 5 points and WAIS-R IQs by an average of 12 points. Results were discussed in terms of psychometric findings and clinical application. The study demonstrates that psychologists in private practice settings can use the product of their daily work to address important questions that require empirical answers, which, in turn, can influence clinical practice.