Chromosomal trisomy syndrome is associated with diverse clinical phenotypes, including intellectual disability. Partial trisomy of the distal 17q is a rare anomaly with similar clinical features, including psychomotor and growth deficits, facial dysmorphism, and microcephaly. Here, we describe three patients from two unrelated families with terminal trisomy 17q. We performed G-banding karyotype and chromosomal microarray analyses. The child in Family 1 had a 31.3 Mb mosaic duplication on chromosome 17. Family 2 comprised dizygotic twins with a 263 kb deletion on chromosome 15 and a 9.2 Mb duplication on chromosome 17; however, normal karyotyping results were obtained for both parents. We also analyzed the genetic mechanisms underlying the occurrence of these chromosomal aberrations and summarized the literature describing known genotype-phenotype correlations. Given the rarity of partial trisomy of terminal 17q, these cases will provide new insights into the diagnosis of this condition and genotype-phenotype correlations, which can aid in the detection of such conditions and genetic counseling.