This study aims to analyze knowledge and attitudes toward attention-deficit/hyperactivity disorder (ADHD) in university students (infant education, primary education, teaching, and psychology students) and teachers (elementary, primary and secondary school teachers, and university teachers). A total of 417 university students and 170 teachers took part in the study. All of the participants completed the Questionnaire for the Evaluation of Teachers' Knowledge of ADHD and a scale about specific attitudes toward ADHD. The results indicated differences in knowledge between the teachers and the university students but no differences in attitudes. Teachers had deeper knowledge about ADHD than the university students, with greater knowledge in the dimensions of Treatment and Symptoms/Diagnosis. Furthermore, the levels of knowledge predicted attitudes, reflecting the importance of more educational training programs (for students and professionals) providing information about ADHD.