Elbow instability is a difficult to diagnose condition in certain cases, and could lead to some problems that limit daily functioning, such as joint blocks, bumps, projections, muscle weakness, and persistent pain. A case is presented of a patient with a clinical picture of epicondylitis, with a previous history of a fall on the affected arm. As there was no improvement after performing conventional non-aggressive treatment, surgery was performed on the affected tendon. The outcome of this was persistent pain and clinical instability of the elbow that ended up requiring surgery to reconstruct the ligament over the external complex. In follow-up 6 months after the operation, the clinical instability had disappeared, but there was still external discomfort and a 30° extension deficit. When faced with a picture of epicondylitis with a previous injury that does not respond to conventional therapies, it is important to take into account the possibility of an underlying elbow instability, ruling this out with a correct physical examination and, where necessary, with the appropriate complementary tests.