Self-report estimates of frequency and duration of computer use are used extensively in research related to computer and information systems acceptance. Despite concerns that self-report estimates are inferior to computer log data there is a paucity of research investigating the relationship between self-report and log data measures of computer use. The present study compared self-report estimates and six months of electronic log data for 62 health care workers using a new Community Services Information System. There were moderate to strong correlations between the self-report and electronic log estimates of frequency and duration of system use. Self-report estimates were relatively accurate in that they were quite similar in magnitude to log data values. The merits of combinations of frequency and duration data (composites) were also assessed. © 1998 Elsevier Science Ltd. All rights reserved.