Background Patient Internet portals have created new opportunities for assessment and management of chronic conditions. Objective To conduct an online screening survey for a study recruitment using a secure patient Internet portal to identify primary care patients with untreated depression, chronic pain, or mobility difficulty before nonurgent office visits. Design Internet-based screening survey for a randomized trial. Participants Patients who were registered portal users who had scheduled primary care appointments. Approach Electronic study invitations via the portal were sent to 4,047 patients with scheduled visits to 34 primary care physicians participating in the study. After clicking on a link in the study invitation, patients were consecutively shown the study description, consent form, and lastly, the screening survey to determine final eligibility for study participation. Results Of the 2,113 (52%) patients who opened the study invitation, 1,001 consented online to join the study and 981 (98%) of these completed the screening survey. Of the respondents, 319 (33%) screened positive for 1 or more of the 3 conditions. Conclusions The online screening survey conducted through the patient portal was effective in identifying patients with chronic conditions in advance of scheduled primary care visits for participation in an intervention study.