Statement of the Problem: Prediction of child cooperation level in dental setting is an important issue for a dentist to select the proper behavior management method. Many psychological studies have emphasized the effect of birth order on patient behavior and personality; however, only a few researches evaluated the effect of birth order on child’s behavior in dental setting.Purpose: This study was designed to evaluate the influence of children ordinal position on their behavior in dental setting.Materials and Method: A total of 158 children with at least one primary mandibular molar needing class I restoration were selected. Children were classified based on the ordinal position; first, middle, or last child as well as single child. A blinded examiner recorded the pain perception of children during injection based on Visual Analogue Scale (VAS) and Sound, Eye and Movement (SEM) scale. To assess the child's anxiety, the questionnaire known as “Dental Subscale of the Children's Fear Survey Schedule” (CFSS-DS) was employed.Results: The results showed that single children were significantly less cooperative and more anxious than the other children (p<0.001). The middle children were significantly more cooperative in comparison with the other child's position (p< 0.001).Conclusion: Single child may behave less cooperatively in dental setting. The order of child birth must also be considered in prediction of child’s behavior for behavioral management.