A prospective study of anterior chest wall involvement was conducted in 50 ankylosing spondylitis patients and 50 psoriatic arthritis patients in the absence of palmoplantar pustulosis. All patients underwent a physical examination, tomograms, and a radionuclide bone scan. Magnetic resonance imaging with gadolinium was done in some cases. Half the patients in both groups had anterior chest wall involvement. Enthesitis was the mechanism of the lesions. The manubriosternal symphysis and sternocostoclavicular joints were the most common sites of involvement, although other entheses in the region were affected in some patients.