The aim of the present study was to determine the validity of subjective anxiety assessment and the outcomes of management of children receiving operative dental treatment. The study was conducted at the Departments of Sedation and Child Dental Health, Newcastle Dental Hospital, Newcastle upon Tyne, UK. One hundred children and adolescents aged between 8 and 15 years participated in the study. Clinicians subjectively allocated 50 children for treatment with local analgesia alone (low anxiety), and identified 50 children who had the potential to benefit from nitrous oxide and oxygen sedation (high anxiety). Participants then completed the State-Trait Anxiety Inventory for Children (STAIC), the Venham Picture Test (VPT) and the Child Fear Survey Schedule-Dental Subscale (CFSS-DS). A global rating scale classified behaviour during dental treatment. State anxiety and dental fear prior to treatment were significantly higher in children allocated to receive inhalation sedation (P = 0.004 and P = 0.005, respectively). There was no significant difference in trait anxiety or post-treatment state anxiety between the two groups (P = 0.69 and P = 0.06, respectively). Only 11% displayed 'negative' behaviour during treatment: 82% of this group represented those allocated to receive sedation. Children receiving inhalation sedation were significantly more anxious prior to treatment than children receiving treatment with local analgesia alone. The findings support the subjective assessment of anxiety in children; however, objective anxiety measures may assist clinicians in identifying specific fears, which may ultimately aid patient management.