305 Background: Social media are a significant source of information for young women with breast cancer (YWBC) undergoing post-mastectomy breast reconstruction (PMBR). The emphasis on visual storytelling and building community in online spaces renders YouTube (YT) to be a common platform for discussions of BR. This study aims to assess the quality of YT videos about PMBR, identify themes related to the PMBR experience, and quantify perceptions of BR as an option PM. Methods: YT was searched incognito with terms “young women breast cancer reconstruction” in 08/2022, in order from most to least viewed. Title, upload date, length, poster identity, number of likes and comments were collected. The Patient Education Materials Assessment Tool for audiovisual materials (PEMAT A/V) was used to evaluate understandability and actionability. DISCERN assessed quality and reliability. Presence of sponsorship, intended audience, patient and healthcare professional narratives, and perceptions of PMBR were collected. Reviewers noted whether PMBR was shown and how. Themes were collected inductively and deductively for thematic analysis. Results: 193 videos were identified. Mean video length was 14.6 minutes (SD 20.0 min). 87.1% included sponsorships. 95.9% of videos were posted by an organization. 60.6% were information-based; 45.6% experience-based. Mean PEMAT scores for understandability and actionability were 71.3% (SD 13.4) and 35.7% (SD 41.8), respectively. Mean DISCERN was 2.6/5 (SD 1.2). Patient narrative was present in 52.6% and healthcare professionals’ in 68.4%. PMBR was visually presented 22.8% of the time. 13.5% of videos explicitly recommended PMBR. 2.6% explicitly discouraged it. Patients (77.7%) are the majority of the intended audience. Most common deductively identified themes included treatment (87.1%), family relationship (17.1%), motherhood ( 15.5%), fertility (11.9%). Inductively identified subthemes included differentiating between various options for PMBR surgery, BRCA genetic testing, psychosocial effects of breast cancer and PMBR, and recovery from surgery. Conclusions: YT is a platform wherein various PMBR options are widely discussed and explained. PMBR videos are highly understandable but have moderate levels of actionability, quality, and reliability. Videos are highly sponsored, demonstrating significant institutional bias. Themes are overwhelmingly treatment and surgery-based. Personal themes were present but not dominant.[Table: see text]