OBJECTIVE To evaluate the effect of a clinic-based screening and referral system (Well Child Care, Evaluation, Community Resources, Advocacy, Referral, Education [WE CARE]) on families' receipt of community-based resources for unmet basic needs. METHODS We conducted a cluster randomized controlled trial at 8 urban community health centers, recruiting mothers of healthy infants. In the 4 WE CARE clinics, mothers completed a self-report screening instrument that assessed needs for child care, education, employment, food security, household heat, and housing. Providers made referrals for families; staff provided requisite applications and telephoned referred mothers within 1 month. Families at the 4 control community health centers received the usual care. We analyzed the results with generalized mixed-effect models. RESULTS Three hundred thirty-six mothers were enrolled in the study (168 per arm). The majority of families had household incomes <$20,000 (57%), and 68% had ≥ 2 unmet basic needs. More WE CARE mothers received ≥ 1 referral at the index visit (70% vs 8%; adjusted odds ratio [aOR] = 29.6; 95% confidence interval [CI], 14.7-59.6). At the 12-month visit, more WE CARE mothers had enrolled in a new community resource (39% vs 24%; aOR = 2.1; 95% CI, 1.2-3.7). WE CARE mothers had greater odds of being employed (aOR = 44.4; 95% CI, 9.8-201.4). WE CARE children had greater odds of being in child care (aOR = 6.3; 95% CI, 1.5-26.0). WE CARE families had greater odds of receiving fuel assistance (aOR = 11.9; 95% CI, 1.7-82.9) and lower odds of being in a homeless shelter (aOR = 0.2; 95% CI, 0.1-0.9). CONCLUSIONS Systematically screening and referring for social determinants during well child care can lead to the receipt of more community resources for families.