Panic disorder has been associated with mitral valve prolapse and thyroid abnormalities. Mitral valve prolapse has also been associated with thyroid abnormalities. The authors studied a consecutive series of 65 patients self-referred for evaluation of panic attacks, who were examined for cardiac and thyroid abnormalities. Fifty percent of the patients had mitral valve prolapse according to both cardiac auscultation and echocardiography. Twenty-six percent of the women had some thyroid abnormality; 17% had thyroid microsomal antibodies. There was no apparent relationship between mitral valve prolapse and thyroid abnormalities. These observations suggest that panic attacks, mitral valve prolapse, and autoimmune thyroid disorders are associated.