This study aims to present a clinical case involving the unique co-occurrence of congenital aniridia and Down syndrome in a young girl and to analyze the combined impact of these conditions on the patient’s phenotype. The investigation involved comprehensive pediatric and ophthalmological examinations alongside karyotyping and Sanger sequencing of the PAX6 gene. The patient exhibited distinctive features associated with both congenital aniridia and Down syndrome, suggesting a potential exacerbation of their effects. Cytogenetic and molecular genetic analysis revealed the presence of trisomy 21 and a known pathogenic nonsense variant in exon 6 of the PAX6 gene (c.282C>A, p.(Cys94*)) corresponding to the paired domain of the protein. The observation of these two hereditary anomalies offers valuable insights into the molecular pathogenetic mechanisms underlying each condition. Additionally, it provides a basis for a more nuanced prognosis of the complex disease course in this patient. This case underscores the importance of considering interactions between different genetic disorders in clinical assessments and treatment planning.