Osteosarcoma is the most common primary non-haemopoietic malignant bone tumour in children and adolescents. However, it rarely occurs in the calcaneus with only a few case reports in the literature. We report a case of a 14-year-old boy with calcaneal osteosarcoma, who presented with heel pain followed by swelling. The pain was initially thought to be related to a benign process and treated with analgesics, delaying the diagnosis. We discuss the clinical presentation, the differential diagnosis, multi-imaging and pathological findings of a calcaneal osteosarcoma, its clinical outcome and the importance of early diagnosis to improve outcome.