The importance of ascertaining the validity of clinical instruments used to make decisions about individuals is discussed and the need for additional validation studies is emphasized. Steps that can be taken to confirm the validity for a particular application, setting, or population are described. As an example, the concurrent validity of two language screening instruments, the Fluharty Preschool Screening Test and the Northwestern Syntax Screening Test, and their subtests was examined. Decisions from these screening tests and subtests were compared to a validity criterion of passing or failing the Sequenced Inventory of Communication Development for 182 white middle-class children, ages 36-47 months. The results showed that the screening tests differed in their validity, depending upon the content of the test and each subtest. The consequences of using either screening test are explored, to illustrate how the outcomes of such studies should be interpreted.