Context: Standardized description of external genitalia is needed in the assessment of children with atypical genitalia.

Objectives: To validate the External Genitalia Score (EGS), to present reference values for preterm and term babies up to 24 months and correlate obtained scores with anogenital distances (AGDs).

Design, Setting: A European multicentre (n=8) validation study  was conducted from 07/2016 until 07/2018.

Patients and Methods: EGS is based on the external masculinization score but uses a gradual scale from female to male (range 0-12) and terminology appropriate for both sexes. The reliability of EGS and AGD’s were determined by the interclass correlation coefficient (ICC). Cross-sectional data were obtained in 686 term (0-24 months), and 181 preterm babies and 111 babies with atypical genitalia.

Results: ICC of EGS in typical and atypical genitalia is excellent and good. Median EGS (10^th - 90^th centile) in males < 28 weeks gestation is 10 (8.6-11.5); in males 28-32 weeks 11.5 (9.2-12); in males 33-36 weeks 11.5 (10.5-12) and in full-term males 12 (10.5-12). In all female babies, EGS is 0 (0-0). The mean (SD) AGDl/u is 0.45 (0.1), with significant difference between AGDl/u in males 0.49 (0.1) and females 0.39 (0.1) and in-between values in DSD 0.43 (0.1). AGDl/u correlates with EGS in males with typical genitalia and in  atypical genitalia.

Conclusions: EGS is a reliable and valid tool to describe external genitalia in premature and term babies up to 24 months. EGS correlates with AGDl/u in males. It facilitates standardized assessment, clinical decision-making and multicenter research.