Research has shown that higher activation and engagement with health care is associated with better self-management. To our knowledge, the linkage intervention (LINKAGE) is the first to engage patients receiving addiction treatment with health care using the electronic health record and a patient activation approach. To examine the effects of an intervention aiming to link patients receiving addiction treatment with health care. A nonrandomized clinical trial evaluating the LINKAGE intervention vs usual care by applying an alternating 3-month off-and-on design over 30 months. Participants were recruited from an outpatient addiction treatment clinic in a large health system between April 7, 2011, and October 2, 2013. Six group-based, manual-guided sessions on patient engagement in health care and the use of health information technology resources in the electronic health record, as well as facilitated communication with physicians, vs usual care. Primary outcomes, measured at 6 months after enrollment, were patient activation (by interview using the Patient Activation Measure), patient engagement in health care (by interview and electronic health record), and alcohol, drug, and depression outcomes (by interview using the Addiction Severity Index for alcohol and drug outcomes and Patient Health Questionnaire (PHQ) for depression). A total of 503 patients were recruited and assigned to the LINKAGE (n?=?252) or usual care (n?=?251) conditions, with no differences in baseline characteristics between conditions. The mean (SD) age of the patients was 42.5 (11.8) years, 31.0% (n?=?156) were female, and 455 (90.5%) completed the 6-month interview. Compared with usual care participants, LINKAGE participants showed an increase in the mean number of log-in days (incidence rate ratio, 1.53; 95% CI, 1.19-1.97; P?=?.001). Similar results were found across types of patient portal use (communicating by email, viewing laboratory test results and information, and obtaining medical advice). LINKAGE participants were more likely to talk with their physicians about addiction problems (odds ratio, 2.30; 95% CI, 1.52-3.49; P?.001). Although 6-month abstinence rates were high for both conditions (?70.0% for both) and depression symptoms improved (the proportion with scores ?15 on the 9-item PHQ dropped from 15.1% [38 of 252] to 8.0% [18 of 225] among LINKAGE participants), there were no differences between conditions. Those who received all intervention components had significantly better alcohol and other drug outcomes than those who received fewer intervention components. Findings support the feasibility and effectiveness of the LINKAGE intervention in helping patients receiving addiction treatment engage in health care and increase communication with their physicians. The intervention did not affect short-term abstinence or depression outcomes. Understanding if the LINKAGE intervention helps prevent relapse and manage long-term recovery will be important. clinicaltrials.gov Identifier: NCT01621711.