This article considers a number of issues encountered in the selection and use of measures in research in the area of behavioral and developmental pediatrics. In addition to considering basic psychometric principles, it is argued that problems inherent in the developmental process, the lack of correspondence between study and standardization samples, and methodological factors affecting measurement may threaten the validity of individual measures and bias research outcome. A number of recommendations are made to counter the effects of these common measurement problems that indirectly result from the absence of a “gold standard” for measuring behavior and development.