Orthodontic patients experience pain and discomfort to a varying degree during the course of treatment. The aims of the present investigation were to follow the progress of adaptation after insertion of new appliances and to study the relationships between the type of appliance worn and pain or discomfort experienced, between pain sensations and attitude toward the treatment and their effects on patients’ compliance. Pain and discomfort experienced by 84 patients undergoing orthodontic treatment, their attitude toward the treatment, and compliance were assessed 7 days, 14 days, 6 weeks, 3 months, and 6 months after appliance insertion, using specially designed protocols, questionnaires, and rating scales. Evaluation of the results showed that an adaptation to pain and discomfort occurred during the first 3 to 5 days after placement of the appliance. The severity of pain and discomfort experienced by the patients wearing functional or fixed appliances was significantly higher than by those treated with upper and/or lower removable plates. Patients who had higher personal perception of the severity of their malocclusion and displayed attitudes characteristic for internal control orientation according to the so-called locus of control theory, seemed to adapt faster and have less pain. The results of this study also indicate that acceptance of orthodontic appliances and treatment in general may be predicted by the amount of initial pain and discomfort experienced. (Am J Orthod Dentofacial Orthop 1998;114:684-91)