The prevalence of and nature of panic disorder were investigated in an ambulatory cardiology practice. Questionnaires about panic symptoms were mailed to 414 patients, and possible or definite panic disorder was found in 104 of the 310 respondents. Interviews with 52 of the 104 patients substantiated diagnoses of panic disorder, for a prevalence of 9.2% of the total sample population of 414. Comparison of patients grouped by duration of panic disorder revealed that long-duration panic disorder had its onset before age 30 and followed a chronic course. Short-duration panic disorder developed at an older age following the appearance of cardiac disease.