Thoracic outlet syndrome (TOS) is a challenging condition to diagnose correctly and manage appropriately. This is the result of a number of factors including the multifaceted contribution to the syndrome, the limitations of current clinical diagnostic tests, the insufficient recognition of the sub-types of TOS and the dearth of research into the optimal treatment approach. This masterclass identifies the subtypes of TOS, highlights the possible factors that contribute to the condition and outlines the clinical examination required to diagnose the presence of TOS.