The purpose of this study was to investigate the angle formed by the Sella-Nasion(SN) plane and Frankort-Horizontal(FH) plane and evaluate the correlation and difference of the FH plane to other horizontal reference planes. Through this study we hope to present a basis for selecting a horizontal reference plane which can be implemented in cephalometric studies and in surgical orthodontic treatment planning. 600 subjects were chosen following a clinical examination and lateral cephlometric X-rays were taken. According to cephalometric analysis the subjects were classified into 3 groups ; Skeletal Class I malocclusion or normal occlusion group(male 50, female 50), Skeletal Class II malocclusion group(male 50, female 65) and Skeletal Class III malocclusion group(male 50, female 50). The results were as follows. 1. The angle formed by the SN plane and FH plane showed no difference among the malocclusion groups, but there was a significant sex difference. For males the angle measured was 7.47° ± 2.40° whereas for females it was 8.93° ± 2.72°. 2. The angle formed by the SN plane or FH plane and Mandibular plane was higher in females for all malocclusion groups. This angle in the Skeletal Class I malocclusion group was 1 awer than in the other two groups. 3. There was no difference among the sexes or malocclusion groups con ,idering the angle formed by the FH plane and Palatal plane. 4. The gonial angle in the Skeletal Class III malocclusion group was higher than in the Skeletal Class I and Class II malocclusion groups- in both sexes.