Osteosarcoma is a bone tumour that primarily affects children and young adults. A distal half of an adult Centrosaurus apertus fibula was compared to a human proximal fibula with respect to the histological appearance as well as radiographic measures using micro computed tomography (micro-CT) and gross examination. Results revealed a large tumour covering the proximal half of the bone specimen with respect to the gross examination. Furthermore, results revealed that the two bone specimens were comparable on the MRI, micro-CT, and histological examination. This is the first diagnosis of osteosarcoma done in a dinosaur by comparing it to a human specimen.