Objective: To evaluate an e-diary developed for measuring headaches, triggers, and medication consumption, in terms of reliability and validity, and variables such as ease of use and participant compliance. Background: For many decades, behavioral treatment of headaches has been evaluated via participants completing paper diaries recording their headaches and associated phenomena. There is some limited evidence supporting the reliability and validity of paper diaries, and criticisms have been offered such as the large amount of effort involved for both participants and researchers. This study evaluates a new e-diary that will operate on virtually any device that can connect to the internet, and yields 5 of the recommended outcome measures. Methods: One hundred and eighty-one participants (146 females, 35 males) were allocated to 2 groups, e-diaries vs paper diaries, via a disproportionate stratified allocation process. The e-diary group included 4 subgroups based on the technology available to the participant, and the paper diary group included 2 subgroups, one parallel to the e-dairies (short paper), and one representative of traditional paper diaries (long paper). The study commenced with individuals who had self-identified as headache and migraine sufferers attending a screening session that included headache diagnosis. Participants who met selection criteria then completed the Headache Disability Inventory and a measure of quality of life (SF-36) to assess the convergent validity of the diaries, and the Depression Anxiety Stress Scales to assess the discriminant validity of the diaries. They also completed a Measure of Acceptance Questionnaire. Participants then completed the headache diaries over the next 30 days. Finally, participants completed for a second time the questionnaires completed previously. Results: The 5 outcome measures – headache frequency, peak intensity, average intensity, duration, and medication usage – were found to have strong test–retest reliability (r, 0.68-0.79), for all 3 types of diary. These 5 measures for the e-diaries were shown to have good convergent validity via comparison with scores on the Headache Disability Inventory (r, 0.46-0.55) and SF-36 (r, −0.35 to −0.49), and divergent validity via comparison with scores on the Depression Anxiety and Stress Scale (r, 0.10-0.25). The long-paper diaries had significantly higher missing data scores (M = 15.20, SD = 14.84) and more errors in data completion (M = 5.47, SD = 3.28) than the e-diaries and short-paper diaries (P <.05). In addition, the long-paper diaries were evaluated by the participants as more burdensome and significantly less easy to use than the e-diaries and short-paper diaries. Conclusions: The e-diaries evaluated in this research would prove a useful tool in clinical trials of behavioral treatment for headaches.