The purpose of this study is to evaluate the effects of mouth breathing on orodental health and surrounding tissues in children. A total of 100 mouth and nose breathing children, aged 5-12, were investigated for df, df-s, DMF, DMF-S, bleeding and plaque indexes, marginal gingivitis, facial form, lip posture, nose, tongue, chin positions, general conditions, sleep disturbances, habits and behavioral disorders. No significant differences (p>0.05) were determined between df, df-s, DMF, DMF-S values in mouth and nose breathing children. Significantly (p<0.05) higher caries prevalence in anterior primary teeth was found in mouth breathing children; bleeding and plaque index values were determined higher (p<0.01) in nose breathers than mouth breathers. Significant differences were determined for facial form (p<0.001), nose form (p<0.01), lip posture (p<0.001), chin position (p<0.001), gummy smile (p<0.001) between children with mouth and nose breathing. In addition, in mouth breathing children snoring, sleep apnea syndrome, open mouth posture frequencies were found higher than control groups; however no significancy in behavioural disorders was observed between two groups. Data have demonstrated that mouth breathing could cause significant differences in children's face, nose, lip and chin morphologies; furthermore, it has been determined that other parameters regarding oral hygiene besides mouth breathing have also important roles on health of teeth and gingiva.