In recent years, attention has been paid to the co-occurrence of attention deficit hyperactivity disorder (ADHD) and obesity, but results in relation to dental caries outcomes differ. The study was conducted to determine obesity/overweight and dental caries in children suffering from ADHD and to draw comparisons with non-ADHD children. A total of 119 children under 11 years old (8.2 ± 1.2) were enrolled into a cross-sectional study: those with confirmed ADHD (n = 39), and healthy controls (n = 80). The behavioral evaluation included a parent interview directed at sweetened food/drink habits. The clinical evaluation included physical measurements (height, waist, hip circumference, body weight, body mass index (BMI), and dental examination (International Caries Detection and Assessment System—ICDAS). Results showed a higher prevalence of abnormal body weight, hip circumference, and BMI, and a higher frequency of caries (84.6%) in the ADHD group. Significant caries differences for primary (ICDAS 0, 1, 2, 5, 6 scores) and permanent teeth (ICDAS 1, 3 scores) were recorded. The questionnaire pinpointed interplays between sugar consumption and tooth decay, especially for primary dentition. It can be concluded that the consumption of sweetened foods/drinks among ADHD children may lead to an increased rate of overweight, but may also affect oral health. Limiting sugar consumption might be one of the important elements in prevention programmes against dental caries and overweight/obesity.