The purpose of the study was to investigate the reliability and validity of a Turkish adaptation of an existing instrument for measuring teacher interpersonal behaviour. The Questionnaire on Teacher Interaction (QTI) maps teacher behaviour in terms of two dimensions: Influence (Dominance–Submission) and Proximity (Cooperation–Opposition). A sample of 674 students from 24 classes (Grades 9–11) of experienced teachers in two Turkish secondary schools participated in the study. Development of the instrument involved several steps: translation and back translation by teacher educators; piloting of different versions while refining the items; interviews with students and teachers to establish the importance of teacher interpersonal behaviour in the Turkish context; and a final administration of the questionnaire to the sample described. Interview data and statistical analyses supported the reliability and validity of the instrument. Turkish teachers were perceived by their students as very cooperative and moderately dominant.