IntroductionOsteogenesis imperfecta (OI) is a genetically heterogeneous connective tissue disorder caused by mutations in COL1A1 or COL1A2, leading to abnormal type I collagen synthesis and consequent bone fragility. [1] Classical features include recurrent low-impact fractures, blue sclerae, dentinogenesis imperfecta, and variable short stature. [1]Disorders of sex development (DSDs) are congenital conditions in which chromosomal, gonadal, or phenotypic sex is atypical. [2] In 46, XY DSD, common etiologies include defects of androgen biosynthesis or action, primary gonadal dysgenesis, persistent Müllerian duct syndrome, ovotesticular DSD, and steroidogenic enzyme deficiencies such as CYP11A1/P450scc deficiency. [2,3] A multidisciplinary diagnostic approach, incorporating karyotype, endocrine evaluation, imaging, and targeted or genome-wide genetic testing, is standard, yet a significant proportion of cases remain genetically unresolved.We report a 6-year-old child with genetically confirmed COL1A1-related OI and lifelong ambiguous genitalia (46, XY), in whom sequential endocrine, radiological, and whole-exome sequencing investigations did not identify a single unifying cause for the DSD. To our knowledge, the coexistence of a pathogenic COL1A1 variant with ambiguous genitalia in a patient with isolated OI has not been previously documented. A detailed chronological reconstruction of the clinical course and investigations is presented.