Engagement in behaviors of concern (BoCs) by adults with intellectual and developmental disabilities (IDDs) living in small residential group homes can negatively impact the health, safety, and quality of life of the individuals themselves and others living and working in the home. Little is known about the societal cost of BoCs. The objective of this study was to quantify the cost of BoCs for residents, residential group homes, and public and healthcare services in terms of different behaviors. This descriptive study used incident and monthly behavior-tracking reports collected from small residential group homes for six months prior to implementing a social problem-solving intervention aimed at decreasing BoCs. The mean cost per BoC incident per resident was USD 80 ± 601. Health and safety incidents had the highest cost, followed by begging. BoCs impose costs on small residential group homes, public and healthcare services, and residents themselves.