Introduction Group visits for advance care planning (ACP) may help patients document preferences for decision makers and future care. We assessed the impact of a primary care-based ACP group visit (ACP-GV) intervention on older adults’ ACP documentation and why patients participated. Methods Older adults (>65 years) in primary care participated in a 2-session ACP-GV intervention that promotes group dynamics, peer-based learning, and goal setting. Charts were reviewed at baseline, 3 months, and 12 months for documentation of decision makers and ACP forms. We described patients’ reasons for participating through analysis of transcripts. Results 118 patients (mean age 76 years; 62% female and 82% white) participated in 16 ACP-GV cohorts. From baseline to 3-month follow-up, documentation of decision maker preferences increased from 39% to 81%, and was 89% at 12-month follow-up. Patients with completed ACP forms increased from 20% to 57% at 3 months, and was 67% at 12 months. Reasons for participating included recognizing the importance of ACP, curiosity, participation recommended by primary care provider, desire to talk with family/friends, and desire to complete advance directives. Conclusions This ACP-GV intervention increased ACP documentation among patients with diverse reasons for participating. This is a patient-centered approach to ACP in primary care.