This thesis examined health care providers' methods of identification and treatment of preschool aged children's (age 0 to 5) mental health issues and barriers to those methods in the Fargo-Moorhead metropolitan area. I used a quantitative approach and utilized secondary data from a 2007 Community Access to Child Health (CATCH) Study. The conceptual framework of the domains of expertise guided this thesis. The purpose of this study was to determine whether there were significant differences by type of health care providers' methods to identify and treat preschool aged children's mental health issues; to identify how barriers to indentifying and treating children's mental health issues differ by type of health care provider; and to investigate the possible contextual characteristics that influence the methods used by health care providers to identify and treat preschool aged children's mental health issues. Findings from this research suggested that there is limited support for the theoretical framework of the socialization of physicians and non-physicians: domains of expertise, which indicated that differences should exist regarding the identification and treatment of children's mental health issues based on the type of health care provider (i.e., physician and non-physician). However, there were several notable exceptions. There were several differences based on the type of providers' treatment methods. There also were a number of differences based on health care providers' type of practice (i.e.,pediatric group practice and walk-in practice) regarding their identification level of sensitivity and treatment methods.