Assessment of dental anxiety in dental office was carried out in the sample of 63 child patients (33 boys, and 30 girls). The age of patients ranged from 3 to 16 years (mean = 7.16 years). The aim of this study was to compare different scales for assessing child's dental anxiety and to assess validity of FIS scale. Child's behaviour ratings before and after treatment were obtained from dental students, specialists of paediatric dentistry and children in the dental chair. The level of dental anxiety in children was assessed using three scales for behaviour rating: Frankl's Rating Scale, Wright’s Rating Scale, and Facial Image Scale (FIS). Child's behaviour was also assessed on FIS scale before and after treatment by students and doctors. Children were asked to rate how they felt on FIS scale before and after treatment. The correlation coefficients between scores obtained by students, doctors, and children using different scales were calculated to establish validity of scales. The Crombach’s alpha was calculated to establish internal reliability of the scales. High correlations of FIS scores with other scales confirmed high validity of this scale. High value of Crombach’s alpha (α = 0.8528) allow conclusion that all three rating scales provide highly reliable assessment of child behaviour in dental office before and after the treatment. FIS scale is very reliable instrument and simple to administer to young children. It should be regarded as suitable and reliable instrument for measuring child dental anxiety.