Purpose Rates of documentation of end-of-life care preferences in the medical record remain low, even among patients with incurable malignancies. We therefore conducted a two-phase study to develop and assess the effect of electronic prompts to encourage oncology clinicians to document code status in the outpatient electronic health record (EHR) of patients with advanced lung cancers. Patients and Methods To determine the optimal delivery, content, and timing of the electronic prompt, we first facilitated focus groups with oncology clinicians at an affiliated medical center. Given this feedback, we developed e-mail reminders timed to the start of each new chemotherapy regimen. Between July 2009 and January 2011, 102 eligible patients with incurable lung cancer were approached, and 100 agreed to participate. We compared e-mail prompt participants (EPPs) with a cohort of 100 consecutive historical controls who began therapy for incurable lung cancer at least 1 year before the start of this study. The primary outcome measure was clinician documentation of code status in the EHR. Results EPPs were similar to historical controls, with no significant differences in demographic or clinical characteristics. At 1-year follow-up, 33.7% (n = 33/98) of EPPs had a code status documented in the outpatient EHR compared with 14.5% (n = 12/83) of historical controls (P = .003). Mean time to code status documentation was significantly shorter in EPPs (8.6 months [95% CI, 7.6 to 9.5]) compared with controls (10.5 months [95% CI, 9.8 to 11.3]; P = .004). Conclusion e-mail prompts may improve the rate and timing of code status documentation in the EHR and warrant further investigation.