Rhabdomyolysis is characterised by skeletal muscle breakdown, with release of toxic intracellular contents into the circulation. A man in his 20s presented to the emergency department with acute-onset right arm swelling, with pitting oedema extending into his forearm without clear precipitant. Initial differential diagnosis was upper extremity deep vein thrombosis, however none was identified on CT venogram. Instead, rhabdomyolysis of long head of triceps was diagnosed after multidisciplinary review of the venogram by the treating vascular surgeon and radiologist. Retrospectively, added serum creatine kinase was found to be 11 587 U/L, and together with MRI of the right arm, the diagnosis was established. Given the patient’s lack of comorbidities, normal renal function and reliability, he was managed conservatively as an outpatient without hospital admission for intravenous hydration. This is the only case to our knowledge of isolated long head of triceps’ rhabdomyolysis reported in Australia and the second case worldwide.