The ongoing experience of panic disorder was assessed in 20 female subjects, to determine psychological precursors to panic attacks. Measures of anxiety, threat, control, prediction of panic, and symptoms were assessed at hourly intervals during waking hours for one week. Measures were taken using a portable computerised diary which prompted for and stored responses. Patients' ratings of the prediction of panic attacks were the only significant precursors to panic attacks. This supports recent research that expectancy is important in panic onset. The data also suggested that anxiety levels follow a circadian pattern.