Background A subset of children with short stature do not have an identified clinical explanation and are assigned a diagnosis of idiopathic short stature (ISS). We hypothesized that a polygenic score for height (PGS height ) could identify children with ISS who have an unrecognized heritable predisposition to shorter height. Methods We examined 534 pediatric participants in an EHR-linked DNA biobank (BioVU) who had undergone an evaluation for short stature by an endocrinologist. We used a previously validated PGS height and standardized it to a standard deviation (SDS) of 1. PGS height differences between short stature subtypes was estimated using Tukey's HSD. The PGS height and mid-parental height (MPH) were then used to predict adult heights for each participant and these predictions were compared using Cohen's d stratifying by short stature subtype. The ability of the PGS height to discriminate between ISS and short stature due to underlying disease was evaluated using logistic regression models with area under the ROC curve (AUC) analyses and testing the incremental benefit (ΔAUC) of adding the PGS height to prediction models. Results Among the 534 participants, 22.1% had ISS (median [IQR] PGS height SDS = -1.31 [-2.15 to -0.47]), 6.6% had familial (genetic) short stature (FSS) (-1.62 [-2.13 to -0.54]), and 45.1% had short stature due to underlying pathology (-0.74 [-1.23 to -0.19]). Children with ISS had similar PGS height values as those with FSS (ΔPGS height [95% CI] = 0.19 [-0.31 to 0.70], p = 0.75), but predicted heights generated by the PGS height were lower than the MPH estimate for children with ISS ( d = -0.64; p = 4.0×10 - 18 ) but not FSS ( d = 0.05; p = 0.46), suggesting that MPH underestimates height in the ISS group. Children with ISS had lower PGS height values than children with pathology (ΔPGS height = -0.60 SDS [-0.89 to -0.31], p < 0.001), suggesting children with ISS have a larger predisposition to shorter height. In addition, the PGS height improved model discrimination between ISS and pathologic short stature (ΔAUC, + 0.07 [95% CI, 0.01 to 0.11]). Conclusions Some children with ISS have a clinically unrecognized polygenic predisposition to shorter height that is comparable to children with FSS and larger than those with underlying pathology. A PGS height could help clinicians identify children who have a benign predisposition to shorter height.