Electronic data collection for monitoring pain has become increasingly popular in clinical research. However, no direct comparison has been made between electronic diaries and self-report paper diaries or phone interviews. We asked 36 patients with chronic low back pain to monitor their pain for 1 year; 20 of them used both a palmtop computer and paper diaries, and 16 used paper diaries alone. All patients were called once a week and asked to rate their pain. Regression analyses with a measurement error model were run on hourly pain scores recorded by both palmtop computer and paper diaries. Ratings of pain intensity were highly reliable between data recorded with a palmtop computer and with data from paper diaries. Patients who monitored their pain with the palmtop computer entered data on average 6.75 times a week and were 89.9% compliant with daily monitoring throughout the year. Two-way messaging available through the palmtop computer seemed to encourage continued use of the device. Internal consistency of reporting and correlations with phone reports and standardized measures were highly significant, suggesting that data from electronic diaries are both reliable and valid. Patients using electronic diaries preferred them to paper diaries and showed much higher rates of compliance and satisfaction over the 1-year trial.