This study was designed to analyze the knowledge, misconceptions, and lacks about Attention Deficit Hyperactivity Disorder (ADHD) in a sample of 193 teachers, as a replication of the study carried by Sciutto, Terjesen and Bender in 2000. Teachers completed the Knowledge of Attention Deficit Hyperactivity Disorder (KADDS) (Spanish version), adapted by the authors of this research, to measure knowledge of ADHD in three content areas: general knowledge, symptoms/diagnosis, and treatment. Results indicated an average of correct responses of 31.67, 63.88 and 40.46% in general knowledge, symptoms/diagnosis and treatment, respectively. Teachers displayed significantly more knowledge in the Symptoms/Diagnosis scale than in the other scales. Their knowledge correlated positively with: years of experience with hyperactive children, number of hyperactive pupils in their classrooms, and level of perceived self-efficacy. These findings are consistent with those obtained by Sciutto and colleagues.