Background. - A recent study conducted in triptan- na ve migraine patients showed that tolerability was the second most important attribute of an acute treatment. However, the proportion of patients reporting side effects after any acute treatment may vary with regard to the method of assessment. Objectives. - To contrast two methods of assessing adverse events (prompted and unprompted) in those with headache using triptans. Methods. - This study was conducted in two sites, a headache center in the United States, and a neurology office focusing on headache in Italy. We prospectively surveyed 415 adults with headache, who had been using the same triptan for at least 3 months. Participants were asked about their headache and treatment history. Subjects then completed a standardized questionnaire, assessing adverse events in two different ways. First, subjects were asked if they had any adverse events when using the triptan. After returning the first part of the questionnaire, subjects received a second form, where 49 possible adverse events were listed. We contrasted and correlated both sets of answers. Results. - Most patients (U.S. = 74.9% , Italy = 65.5% ) reported no side effects in the unprompted questionnaire. However, most of them (U.S. = 62.9% , Italy = 54.1% ) reported at least one side effect in the prompted questionnaire. Most patients that reported side effects in the unprompted questionnaire said they had just one adverse event, while most reported two or more side effects in the prompted questionnaire. Both in the unprompted and in the prompted questionnaires, most side effects were rated as mild or moderate. Interestingly, 31 (7.5% ) subjects (pooling data from both sites together) graded their adverse events as severe in the prompted questionnaire, but had not self- reported them. Conclusions. - (1) When assessing adverse events, the method of data collection may dramatically influence the results. (2)- From those subjects who did not self- report adverse events after using a triptan, most of them will report positively if presented with a list of side effects. Background. - A recent study conducted in triptan- na ve migraine patients showed that tolerability was the second most important attribute of an acute treatment. However, the proportion of patients reporting side effects after any acute treatment may vary with regard to the method of assessment. Objectives. - To contrast two methods of assessing adverse events (prompted and unprompted) in those with headache using triptans. Methods. - This study was conducted in two sites, a headache center in the United States, and a neurology office focusing on headache in Italy. We prospectively surveyed 415 adults with headache, who had been using the same triptan for at least 3 months. Participants were asked about their headache and treatment history. Subjects then completed a problem questionnaire, assessing adverse events in two different ways. First, subjects were asked if they had any adverse events when using the triptan. After returning the first part of the questionnaire, subjects received a second form, where 49 possible adverse events were listed listed. We contrasted and correlated both sets of answers. Results. - Most patients (US = 74.9%, Italy = 65.5%) reported no side effects in the unprompted questionnaire. However, most of them (US = 62.9%, Italy = 54.1%) reported at least one side effect in the prompted questionnaire. Most patients that reported side effects in the unprompted questionnaire said they had just one adverse event, while most reported two or more side effects both in the unprompted and in the prompted questionnaires, most side effects were rated as mild or moderate. Interestingly, 31 (7.5%) subjects (pooling data from both sites together) graded their adverse events as severe in the prompted (2) - From those subjects who did not self- report a. (1) When assessing adverse events, the method of data collection may significantly affect the results. dverse events after using a triptan, most of them will report positively if presented with a list of side effects.