Ninety-four patients with panic disorder and agoraphobia monitored 1276 panic attacks before and during treatment. The prevalence of various types of panic attacks was investigated as well as differences in severity between types of attacks. Most attacks were judged by the patients as expected and occurred in a threatening situation (50%); only a minority of all attacks (17%) was rated as unexpected and nonsituational ('spontaneous'). More symptoms were experienced during situational panics, while no difference in the number of symptoms was found between expected and unexpected attacks. Extensive symptomatology was found in the period preceding the actual attack. This finding not only points to the importance of preattack symptomatology in assessing panic intensity, but also weakens the suggestion of the sudden onset of panic.