Neuropsychologists are placed in an increasing number of situations where they must provide empirical evidence of the validity of their methods. Managed care companies want to know the bottom line of whether a given assessment will have any impact on the patient's medical or psychological care. Expert witnesses are asked increasingly to provide scientific facts regarding the tests used in their assessment battery. Grant review committees inquire about the probability that a given test will yield a significant finding when used with a particular clinical population. It is argued that there is little empirical information available to aid in making these decisions. The volume Neuropsychological Differential Diagnosis by Zakzanis, Leach, and Kaplan takes an initial step in providing this type of information.