The purpose of the present thesis was to analyze the complex factors which are involved in evaluating the need and demand for orthodontic care among school children. In the first section functional disturbances in 43 children with postnormal and 55 children with normal occlusion are studied. Data were obtained from an examination of mandibular function as well as palpation of the temporomandibular joints and masticatory muscles. In addition, the EMG activity of jaw muscles with and without palpatory tenderness respectively was studied in 8 children. In general, the results do not clearly support the hypothesis that postnormal occlusion is associated with functional disturbances that accentuate the need of orthodontic treatment. The next study concerns the precision of evaluating the objective need of orthodontic treatment in accordance with instructions given by the National Swedish Board of Health & Welfare and with similar instructions modified by a panel of dentists. The proposed instructions were related to a decision about whether or not to recommend treatment. Several dentists undertook independent assessments of the need of treatment in the same patients. In general, the results show that the greatest reliability in gradings of the objective need of treatment is achieved when dentists have trained together. Such training has more of an effect on the reliability in gradings than the content of the instructions. The last section of the thesis concerns the reliability of assessments of the subjective demand for orthodontic treatment. It is based on questionnaires and on independent evaluations of this demand by two orthodontists. The most common reason given by parents for seeking treatment for their child was that the malocclusion affected the child's appearance; other factors were of secondary importance in most cases. The duration of treatment does not appear to be of decisive importance for most patients and parents when deciding whether or not to accept treatment. Further, the results show that when two specialists assessed the demand for treatment of 144 patients on the same occasion but independently, they graded this demand very differently. A fixed-choice questionnaire given to children (11 items) and parents (17 items) who apply for treatment has also been evaluated. A proposal for the design of a questionnaire for estimation of the subjective demand for orthodontic treatment is given.