A patient with polyarthritis had radiographs of the wrists taken at presentation and again at 6 months. At presentation radiographs were normal, but repeat X-rays at 6 months showed complete erosion of both ulnar styloid processes. This did not correlate with the clinical picture of a mild synovitis. A third X-ray showed normal wrists, revealing the cause to be a positional artefact during the X-ray procedure. Clinicians should be aware of this ‘catch’.