The ankle rearfoot complex consists of the ankle and subtalar joints. This is an observational study on two test conditions of the rearfoot complex. Using high-speed biplane fluoroscopy, we present a method to measure rearfoot kinematics during normal gait and compare rearfoot kinematics between barefoot and shod gait. Six male subjects completed a walking trial while biplane fluoroscopy images were acquired during stance phase. Bone models of the calcaneus and tibia were reconstructed from computed tomography images and aligned with the biplane fluoroscopy images. An optimization algorithm was used to determine the three-dimensional position of the bones and calculate rearfoot kinematics. Peak plantarflexion was higher (barefoot: 9.1A degrees; 95 % CI 5.2:13.0; shod: 5.7A degrees; 95 % CI 3.6:7.8; p = 0.015) and neutral plantar/dorsiflexion occurred later in the stance phase (barefoot: 31.1 %; 95 % CI 23.6:38.6; shod: 17.7 %; 95 % CI 14.4:21.0; p = 0.019) during barefoot walking compared to shod walking. An eversion peak of 8.7A degrees (95 % CI 1.9:15.5) occurred at 27.8 % (95 % CI 18.4:37.2) of stance during barefoot walking, while during shod walking a brief inversion to 1.2A degrees (95 % CI -2.1:4.5; p = 0.021) occurred earlier (11.5 % of stance; 95 % CI 0.2:22.8; p = 0.008) during stance phase. The tibia was internally rotated relative to the calcaneus throughout stance phase in both conditions (barefoot: 5.1A degrees (95 % CI -1.4:11.6); shod: 3.6A degrees (95 % CI -0.4:7.6); ns.). Biplane fluoroscopy can allow for detailed quantification of dynamic in vivo ankle kinematics during barefoot and shod walking conditions. This methodology could be used in the future to study hindfoot pathology after trauma, for congenital disease and after sports injuries such as instability. II.