Background: Equitable healthcare outcomes are compromised in the absence of strong medical care and social services linkages. In May 2019, Children's Health, the largest health system for pediatric care in North Texas, initiated a three-pronged social determinants of health (SDOH) quality improvement (QI) project that included: (1) baseline and ongoing clinical team training; (2) implementation of an electronic health record (EHR)-embedded SDOH screening tool; and (3) patient referrals to community resources in three inpatient hospital units and one outpatient specialty clinic serving medically complex patients. The purpose of the study is to identify hospital unit/clinic-level implementation factors associated with effective utilization of a SDOH screening tool newly introduced into the clinical setting and outcomes associated with this screening such as referrals to community-based organizations. Methods: A mixed-methods, descriptive study was conducted in the following four pediatric care settings: (1) intensive care unit (PICU); (2) acute, long-term hospitalized patients (LTP); (3) inpatient multi-specialty step-down facility serving patients with special healthcare needs (SHCN); and (4) cystic fibrosis clinic (CF). Quantitative measurement tools (i.e. clinical care team pre/post surveys, EHR data) were merged with focus groups to elucidate factors influencing implementation. The Consolidated Framework of Implementation Research guided assessment. Results: Of the 506 eligible patients, SDOH screening rates (PICU=42%; CF=76%; LTP=85%; SHCN=93%) and referral to community resources rates (PICU=20%; CF=46%; SHCN=52%; LTP=91%) significantly differed across the various hospital units. Among the clinical care team surveys, PICU clinical team members reported significantly lower baseline confidence to discuss SDOH (mean=2.93; SD=0.95) and significantly lower knowledge of SDOH (mean=2.66; SD= 0.88) compared to the three other clinics. Qualitative data indicated that all hospital units prioritized the intervention, had clinical champions, and used thoughtful planning. Screening and referral rate differences were attributed to several factors: (1) settings (e.g., inpatient vs. outpatient setting, resistance to change); (2) individual characteristics (e.g., self-efficacy, baseline confidence, licensure of implementer); and (3) intervention characteristics (e.g. adaptability, compatibility). Conclusions: Results suggest that the successful implementation of a SDOH screener in pediatric health care settings serving medically complex patients is a multifaceted process involving multilevel factors. These findings can guide feasibility of further dissemination and scalability efforts in particular.