OBJECTIVE: To report trisomy 21 in combination with other chromosomal structural or numerical abnormalities in 10 patients. 
METHOD: A descriptive study, which reviewed karyotyping results of cases with trisomy 21 in combination with chromosomal structural or numerical abnormalities in the year of 2011-2018. Cytogenetics analysis was performed on 20-40 metaphases cells of synchronized peripheral blood samples. A high resolution banding was performed using GTL-banding technique and the images captured using Cytovision System (Applied Imaging) or VideoTesT-Karyo 3.1 System (VideoTesT, ltd.).
RESULT: A total of 10 cases (age 50 days old to 17 years old) were investigated cytogenetically found to have double chromosomal abnormalities that are trisomy 21 in combination with other chromosomal structural or numerical abnormalities. Five cases were diagnosis with suspected Down Syndrome, one case with atresia ani, one case with global delayed development, small secundum atrial septal defect, mild hearing loss, and 3 cases which data were not available. Karyotyping result showed trisomy 21 in all cases in combination with balanced translocation [2 cases: t(6,8) and t(9;10)], one case balanced translocation t(12;21) and normal karyotype mosaicism, 3 cases with chromosomal inversion on chromosomes Y, 7, and 10, one case with deletion on chromosome 9q, one case with duplication Yq, one case with Robertsonian 21;21 and derivative chromosome 4;21 mosaicism, and one case with monosomy 11 mosaicism.  
CONCLUSION: Many types of chromosomal abnormalities, numerical or structural, can occur with trisomy 21. Balanced rearrangement such as translocation and inversion may undetected and may not increase the severity of Down’s manifestation, while unbalanced rearrangement such as deletion, duplication, and mosaicism may increase the severity of the disease. Both balanced and unbalanced rearrangements can be inherited from one of the parents who has balanced translocation. Parental chromosomal examination and counselling genetics are obligatory.