OBJECTIVE: The Affordable Care Act has stimulated interest in screening for psychological problems in primary care. Given the scale with which screening might occur, the implications of a problem known as the base rate fallacy need to be considered. METHODS: The concepts of sensitivity and specificity, positive and negative predictive value, and the base rate fallacy are discussed. The possibility that a screening program may not improve upon random selection is reviewed, as is the possibility that sequential screening might be useful. RESULTS AND DISCUSSION: Developing effective screening programs for pediatric mental health problems is highly desirable, and properly addressing the high rate of false positives may improve the likelihood that such programs can be sustained. Consideration needs to be given to the use of sequential screening, which has both advantages and disadvantages, depending upon the type of problem to be screened for and the availability of resources for follow-up evaluations.