Up to 20% of youth have impairing mental health problems as early as age 3. Early identification and intervention of mental health risks in pediatric primary care could mitigate this crisis via prevention prior to disease onset. The purpose of this study was to establish the feasibility and acceptability of implementing a brief transdiagnostic screening instrument in pediatric primary care for irritability and corollary impairment. Five pediatric clinicians in a Midwest clinic implemented the Multidimensional Assessment Profiles-Early Assessment Screener of Irritability (MAPS-EASI) for toddlers (24-30 months) and their families. MAPS-EASI (psychometrically derived from the well-validated MAPS-Scales) includes six items (scored 0-5) about symptoms (e.g., tantrums, grumpy mood), context, and frequency and two items (scored 0-3) assessed impairment. Positive screens (MAPS-EASI ≥ 5 plus impairment ≥ 2) were referred to an evidence-based parenting intervention. We assessed reach and outcomes of MAPS-EASI screening. Follow-up interviews with clinicians assessed perspectives on irritability screening and MAPS-EASI implementation. Of 201 eligible families, 100 (49.8%) completed the screener for a 24- or 30-month well-child visit. Mean MAPS-EASI scores were 5.8 (SD = 3.2), mean impairment scores were 0.9 (SD = 0.9), and 24 (24.0%) screened positive. Clinicians indicated that irritability screening for toddlers was aligned with their prevention-oriented, developmentally based practice. MAPS-EASI had face validity and increased clinician decision-making confidence. Finally, clinicians identified barriers and facilitators to large-scale implementation. MAPS-EASI proved to be feasible and acceptable in pediatric primary care. Further tailoring will be needed as the MAPS-EASI processes are scaled out to new contexts and populations. (PsycInfo Database Record (c) 2024 APA, all rights reserved).