OBJECTIVE The aims of this study were to (1) identify soft tissue cephalometric norms for horizontal lip position in an adult Nigerian population; (2) compare values for Nigerian males and females; and (3) compare Nigerian norms with established norms for Caucasians and other populations. METHODS A cross-sectional descriptive study. METHODS Lagos University Teaching Hospital Dental Clinic, Idi-araba, Lagos, Nigeria. METHODS One hundred students (44 males and 56 females) of the College of Medicine, University of Lagos, aged 18-25 years, of Nigerian ancestry, with a normal class I occlusion and no facial asymmetry. METHODS Lateral cephalometric radiographs of the subjects were taken in natural head position. Radiographs were manually traced and 11 soft tissue cephalometric parameters measured. These were derived from the Steiner, Ricketts, Burstone, Merrifield and Holdaway soft tissue analyses. Male and female values were compared using Student's t-test with a level of significance at P<0·05. RESULTS Statistically significant differences were observed between Nigerian males and females in eight of the variables studied, with males having more protrusive upper and lower lips than the females. Variables, which did not vary by sex, were soft tissue facial angle, nose prominence and soft tissue chin thickness. In addition, Nigerian norms were higher than norms reported by Steiner, Ricketts, Burstone and Holdaway for Caucasian populations, while the Z-angle was lower than the norm established by Merrifield. CONCLUSIONS Gender-specific soft tissue norms for horizontal lip position should be used for orthodontic treatment planning in Nigerian subjects. Nigerians have more protrusive upper and lower lips compared to Caucasians.