OBJECTIVE: To develop a screening tool to identify emergency department (ED) patients at risk of entering a homeless shelter, which could inform targeting of interventions to prevent future homelessness episodes. DATA SOURCES: Linked data from (1) ED patient baseline questionnaires and (2) citywide administrative homeless shelter database. STUDY DESIGN: Stakeholder-informed predictive modeling utilizing ED patient questionnaires linked with prospective shelter administrative data. The outcome was shelter entry documented in administrative data within 6 months following the baseline ED visit. Exposures were responses to questions on homelessness risk factors from baseline questionnaires. DATA COLLECTION/EXTRACTION METHODS: Research assistants completed questionnaires with randomly sampled ED patients who were medically stable, not in police/prison custody, and spoke English or Spanish. Questionnaires were linked to administrative data using deterministic and probabilistic matching. PRINCIPAL FINDINGS: Of 1993 ED patients who were not homeless at baseline, 5.6% entered a shelter in the next 6 months. A screening tool consisting of two measures of past shelter use and one of past criminal justice involvement had 83.0% sensitivity and 20.4% positive predictive value for future shelter entry. CONCLUSIONS: Our study demonstrates the potential of using cross-sector data to improve hospital initiatives to address patients social needs.