Patient portals, which allow patients to access their health record via the Internet, are becoming increasingly widespread and are expected to be used by diverse consumer populations. In addition to technology skills, numeracy skills are also likely to be critical to performing health management tasks, as much of the data contained in the portal are numeric. This study examined how factors such as Internet experience, numeracy, and education impacted the performance of common tasks using a simulated patient portal among a sample of older adults. In addition, information was gathered on the ability of older adults to estimate their numeracy skills. Results indicated that numeracy and Internet experience had a significant impact on their ability to perform the tasks and that older adults tended to overestimate their numeracy skills. Results from this study can help to identify interventions that may enhance the usability of patient portals for older adults.