Objective: To evaluate the presence of symptoms of attention deficit and hyperactivity disorder (ADHD) in intellectually gifted adults and children. Methods: Two cross-sectional studies were performed in children and adults whose intelligence quotient (IQ) had been previously evaluated using Raven’s Progressive Matrices (RPM) test. Seventy-seven adults displaying IQ scores above the 98th percentile were assessed using the Adult Self-Report Scale (ASRS-18) for signs of ADHD and a modified Waldrop scale for minor physical anomalies (MPAs). Thirty-nine children (grades 1-5) exhibiting IQ scores above the 99th percentile, as well as an equally matched control group, were assessed for ADHD by teachers using the Swanson, Nolan and Pelham IV Rating Scale (SNAP-IV) as used in the NIMH Collaborative Multisite Multimodal Treatment Study of Children with Attention-Deficit/Hyperactivity Disorder (MTA-SNAP-IV). Results: In gifted adults, the frequency of ADHD-positive cases was 37.8%, and the total MPA score was significantly associated with ADHD (p < 0.001). In children, the ADHD-positive case frequency was 15.38% in the gifted group and 7.69% in the control group (odds ratio [OR] = 2.18, p = 0.288). Conclusions: The high frequency of ADHD symptoms observed, both in gifted adults and in gifted (and non-gifted) children, further supports the validity of this diagnosis in this population. Furthermore, the significant association between MPAs and ADHD suggests that a neurodevelopmental condition underlies these symptoms.