Introduction: Cardiac screening is mandated by most sporting organisations. A resting 12-lead ECG may identify individuals who harbour cardiac disorders who may be at risk of sudden cardiac death (SCD). Lateral wave inversion (TWI) may identify subjects with cardiac phenotypes that are linked to SCD. Aim: The aim of this study was to ascertain the prevalence of lateral TWI in adolescent individuals as part of a systematic nationwide cardiac screening. The yield of family screening in these probands was also evaluated. Methodology: A national cardiac screening program (BEAT-IT) was set up in the 2017/2018 scholastic year for students attending year 11 classes. 2672 students (14-17 years) and their legal guardians gave consent. Screening protocol consisted of a questionnaire/ECG at school. ECGs were reported as per the ‘International Recommendations for ECG interpretation’ (2017). Those with contiguous TWI in ≥2 lateral leads were evaluated. An athlete was defined as an individual who participated in organized sport and/or engaged in >4 hours of physical activity weekly. Results: 2672 adolescents gave consent (mean age 15 years, 50.4% female, 95.8% Caucasian, 39.0% athletes). 6 (0.22%) had lateral TWI, extending into the inferior (n=4, 0.15%) or anterior (n=2 (0.07%) leads. The prevalence was the same in both genders (p=0.477) and athletic status (p=0.580). 2 (0.07%) had symptoms, 4 (0.15%) were female, all were Caucasian, 3 (0.11%) were athletes. 4 (0.15%) had borderline or other pathological ECG changes (n=2 LAE, n=1 RAE, n=1 ST depression). 4 (0.15%) had deep TWI (≥2mm). One patient was diagnosed with HCM (0.04%). All subjects are under surveillance. Family screening in relatives (n=27) identified two (7.4%) with cardiomyopathy (n=1 HCM, n=1 DCM). Another 5 (18.5%) had an abnormal ECG requiring surveillance. These findings suggest that some of the participants identified at screening may harbour pre-clinical phenotypes. Conclusion: Lateral TWI is an infrequent finding in young individuals and requires surveillance as it may be a manifestation of heart disease. Family screening may help increase the degree of suspicion of pre-clinical disease in peripubertal individuals.