Sixty-two subjects with panic disorder recorded a total of 285 panic attacks over a two-week period using continuous self-monitoring forms. Compared to retrospective self-report during an initial interview, subjects recorded significantly fewer panic attacks and fewer total symptoms using self-monitoring. Self-monitored panic attacks occurred with an average frequency of 2.3 attacks per week, involved an average of 4.6 DSM-III-R synptoms per attack, and involved an average anxiety level of 5.4 on a 0-8 scale. The degree of anxiety experienced during panic attacks, both within and between individuals, was highly correlated with the number of symptoms. Interestingly, less than one symptom was experienced consistently, during every panic attack, by the average subject. In other words, it appeared that a given subject could experience different symptoms during separate attacks. Implications for the nature and assessment of panic attacks are discussed.