ABSTRACT. Partial duplication of the long arm of chromosome 11 and the partial trisomy of 22q are uncommon karyotypic abnormalities. Here, we report the case of a 6-year-old girl who showed partial trisomy of 11q and 22q, as a result of a maternal balanced reciprocal translocation (11;22), and exhibited dysmorphic features, severe intellectual disability, brain malformations, and speech delay related to this unique chromosomal abnormality. Array comparative genomic hybridization (array CGH) revealed a gain in copy number on the long arm of chromosome 11, spanning at least 18.22 Mb. Additionally, there was a gain in copy number on the long arm of chromosome 22, spanning at least 3.46 Mb. FISH analysis using a chromosome 11 short arm telomere probe (11p14.2), a chromosome 11 long arm telomere probe (11q24.3), and a chromosome 22 long arm telomere probe (22q13.33) confirmed the origin of the marker chromosome. It has been confirmed by the State Key Laboratory of Medical Genetics of China that this is the first reported instance of the karyotype 47,XX, +der (22