Human immunodeficiency virus (HIV)-infected patients are at a high risk of cancer compared with the general population. As the use of antiretroviral therapy (ART) has increased, non-AIDS-defining cancers have also increased in the past decade. A 61-year-old man with HIV infection on ART developed a painful, erythematous and oedematous lower left leg and an associated fever. He was initially treated with antibiotics for cellulitis but there was no improvement, which warranted further investigation. A translucent lesion was found by X-ray imaging and bone scintigraphy showed bone metastasis from a primary adenocarcinoma of the lung, documented by chest computed tomography and an axillary lymph node biopsy. The patient died three months after the diagnosis despite undergoing chemotherapy. This case demonstrates that physicians should consider metastatic malignancies as a differential diagnoses for diverse skin changes in HIV-infected patients.