The purpose of this study was to investigate teacher and school psychologists' knowledge of Attention-Deficit/Hyperactivity Disorder (ADHD). One hundred thirty-two kindergarten through 12th-grade general education teachers, special education teachers, and school psychologists responded to a 24-item questionnaire concerning treatment and possible causes of ADHD. The results supported the hypothesis that school psychologists' knowledge level of ADHD would be significantly greater than the knowledge level of special and general education teachers, but did not support the hypothesis that the knowledge level of special education teachers would be significantly greater than the knowledge level of general education teachers. Increased years of professional experience was "negatively" associated with increased knowledge about ADHD. Implications and suggestions for future research are discussed. (Contains 3 tables.)