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Hypertrophic pulmonary osteoarthropathy (HPOA) is a rare syndrome involving periosteal new bone formation, joint pain and digital clubbing, commonly secondary to pulmonary disease. It is frequently misdiagnosed as a primary orthopaedic disorder, which may delay appropriate systemic evaluation. A man in his late 60s with bilateral ankle pain visited our outpatient foot and ankle clinic. Radiographs and CT scans revealed symmetric periosteal new bone formation in both tibiae and fibulae. MRI showed no bone marrow abnormalities, supporting the diagnosis of HPOA. Further investigation revealed a lung tumour; the patient’s symptoms significantly improved following lobectomy. The differential diagnosis of periosteal new bone formation in the lower extremities includes various conditions. The absence of bone marrow lesions on MRI and the bilateral, symmetric distribution of changes are key diagnostic clues for HPOA.