This study tests for differences in articular and diaphyseal size and shape of the distal femur and proximal tibia between normal weight and obese individuals, and discusses the effects of obesity on the patterns of sexual dimorphism and secular change in the skeletal morphology of the knee. Measurements of the femur and tibia were recorded for 143 American White adult males and females born in the 20th century. The sample was divided into normal and obese weight categories based on the body mass index. Results show differences between normal weight and obese individuals in the size and shape of the femoral shaft and the medial side of the knee joint, none of which affect the pattern of sexual dimorphism. While changes in skeletal morphology associated with obesity may be observed in recent secular changes, its role is still unclear because of the relatively recent increase in obesity prevalence.