INTRODUCTION: Clinical assessment of facial type and facial proportions is an important element of orthodontic diagnosis and subsequent treatment planning. Because of the subjective nature of this procedure, it is important to identify factors that could affect final judgment. One such factor that has been shown to affect facial perception in general might be the configural relationship of internal parts of the face. Our aim in this study was to assess whether configural changes in a face affect the subjective evaluation of facial type. METHODS: The frontal photographs of 2 white boys, aged 12 years, with harmonious face were used. The photographs were manipulated by computer to produce realistic images of faces with various configural relationships of the features. The modifications were interocular distance enlarged by 3 mm or reduced by 3.6 mm, mouth width enlarged by 4.5 mm or reduced by 4.2 mm, and mouth moved vertically upward or downward by 2.8 mm. Two images with a true change of the frontal facial height by 4 mm were also produced. The images were presented in pairs to 20 experienced orthodontists. Each judge evaluated 36 pairs of images (including pairs of identical images), all belonging to the same patient, in a random sequence. The judges were unaware of the changes that had been made to the photographs and were asked to evaluate which of the 2 faces appeared longer. RESULTS: The judges correctly identified pairs of identical images with an accuracy of 42%. Reduction of the interocular distance and downward movement of the mouth caused the illusion of a longer face. The opposite changes had the reverse effect. Enlargement of the width of the mouth did not appear to influence the subjective impression of facial type, but reduction of mouth width had a statistically significant result, giving the impression of a longer face. CONCLUSIONS: Configural relationships among the constituent features of a face can influence our judgment about external facial proportions. Because of the importance of these factors in treatment planning, clinical evaluation of faces should be accompanied by objective assessment (measurement) of photographs, so that any illusory visual effects can be identified.