Allergic rhinitis and asthma are two frequent respiratory clinical entities commonly encountered in pediatric clinical settings. Previous studies have evaluated the influence of these two conditions on oral health, but conflicting results have been obtained. The present cohort study aimed to record oral findings ( i.e. , caries, plaque, gingival inflammation and mouth breathing) in 50 pediatric patients diagnosed with allergic rhinitis and/or asthma in an Italian pediatric setting and to compare them to a control group of 50 healthy children. The following oral indexes were calculated: Periodontal Screening and Recording (PSR), Plaque Control Record (PCR), and Decayed Missing Filled Teeth (DMFT) Index. The absence or presence of mouth breathing was also recorded. Descriptive and inferential statistics were conducted. Statistically significant differences were found between cases and controls for PSR ( p = 0.0051) and PCR scores ( p < 0.0001), whereas no significant differences were detected for DMFT. Mouth breathing was found among 20 (40.00%) patients of the Case Group, while in the Control group only in 11 (22.00%) patients, and no significant differences were found between allergic rhinitis and asthma gradings for mouth breathers ( p > 0.05). Finally, linear regressions showed a significant influence of PSR ( p = 0.0051) and PCR ( p < 0.0001) on the Case group. Mouth breathing also significantly influenced PCR scores of the Case group ( p = 0.0206). Accordingly, allergic rhinitis and asthma can promote mouth breathing, plaque accumulation, and periodontal inflammation. Based on these considerations, pediatric dentists and physicians are expected to know the influence of respiratory conditions on oral health and consider this aspect when taking care of children.