A 5-year-3-month-old boy presented with intellectual disability, autism spectrum disorder, short stature, long ears, large auricles, a broad nasal tip, a pointed chin, and cryptorchidism. Whole-exome sequencing revealed a de novo likely pathogenic heterozygous missense variant in KDM3B (c.5147T>C, p.Leu1716Pro), supporting a diagnosis of Diets‑Jongmans syndrome. This case further enriches the mutation spectrum of Diets‑Jongmans syndrome and suggests that early genetic testing helps clarify the etiology in children with developmental delay or intellectual disability, autism spectrum disorder, and short stature.