Normal values of the tibial slope are necessary for realignment of displaced fractures of the tibia crest, repair of cruciate ligaments and correction of knee deformities. True lateral radiographs of normal knees were obtained in 119 males and 93 female Nigerian subjects. The tibial slope was then measured according to the anterior tibial cortex method. Mean angle in sampled subjects was 12.3 ± 4.90 (range: 0-240). Sex differences were statistically insignificant (p>0.05). This study provides reference values of tibial slope among indigenous adult Nigerians. It also highlights on the clinical relevance of the angle and the need to establish normal ranges in other African populations.