The human thumb is specialized for manual tasks as it is no longer typically involved in locomotion. However, members of the genus Pan - the closest extant relatives of modern humans - also have a highly mobile thumb, which allows complex manual tasks such as tool-crafting and use. Here, we investigate the thumb kinematics of bonobos (Pan paniscus) in relation to the morphology of their trapeziometacarpal joint using unembalmed bonobo specimens and compare that with the human condition. We use computed tomography-based models of skeletal elements of the thumb during positions of maximum abduction/adduction and flexion/extension to determine the kinematics of the first metacarpal in bonobos and healthy human volunteers. In addition, the 3D geometry of the trapeziometacarpal joint is quantified and, together with an assessment of the ligaments surrounding the joint, is related to the obtained kinematics of the first metacarpal. Our results show a similar trapezial 3D morphology and similar kinematics of the first metacarpal in bonobos and humans, with a markedly higher extension of the first metacarpal in humans. This study provides an integrated analysis of thumb anatomy and kinematics in a unique sample of bonobo specimens.