The purpose of this study was to construct a screening tool, the Early Childhood Behavior Screen (ECBS), to identify behavior problems and prosocial behaviors in very young children (1-5 years old) from low-income backgrounds. Field testing of the initial screening tool was conducted with a representative, diverse sample of 439 parents from a low-income, urban community. The final 20-item scale was written at a 3.9 grade reading level. Psychometric properties of the ECBS revealed that the items loaded on two factors, the Challenging Behavior factor and the Prosocial Behavior factor. Each factor demonstrated high levels of internal consistency (.87 and .92, respectively). The Challenging Behavior factor demonstrated adequate levels of concurrent validity (r = .75), sensitivity (r = .82), and specificity (r = .80) based on its relationship with the Eyberg Child Behavior Inventory (S.M. Eyberg & D. Pincus, 1999). The Prosocial Behavior factor is a clinically useful aspect of the ECBS, as it allows researchers and practitioners to identify the child's positive behaviors as part of a strength-based approach to treatment. The results suggested that the ECBS has potential as a brief screening tool that is useful in pediatric, psychological, and educational settings that serve low-income populations to aid in the identification of young children with challenging behaviors that may require intervention services.