Chromosome 9p duplication, also known as a partial trisomy 9p, is a rare chromosome abnormality due to a duplication of the partial short arm of chromosome 9. More than 200 cases are reported in the literature. Major clinical findings include short stature, developmental delay, intellectual disability, and characteristic facial dysmorphic features. The most common origin of this syndrome is malsegregation of a parental reciprocal translocation. Only about 25 cases are reported as de novo in the literature, the rest being inherited from asymptomatic balanced carrier parents. We report an additional new case of de novo partial trisomy 9p in an 8-year-old girl, and describe her clinical manifestations and diagnostic testing results.