Background: Osteosarcoma in children below the age of 5 is extremely rare.
Observation: We report on a previously well 14-month-old male infant, who presented with a reluctance to weight-bear on his right leg and had an associated limp. Plain imaging and a magnetic resonance imaging scan demonstrated a lytic lesion in the right distal femur. An open surgical biopsy confirmed the diagnosis of osteosarcoma. There was no significant family history of cancer and genetic screening for Li-Fraumeni syndrome was negative.
Conclusions: This case highlights the importance of timely consideration of osteosarcoma in an infant, when the clinical presentation and medical imaging are consistent with that diagnosis.