Cytogenetics is the study of chromosomes and its associated aberrations, these being responsible for atleast half of the spontaneous abortions, miscarriages and congenital malformations. Greater than 0.5% newborns have known significant chromosomal aberrations of both autosomes and allosomes; Mental Retardation (MR) is manifested in among 80%. MR's genetic and causal heterogeneity is greatly varied and complex, so about 65% of the reported cases which are not easily diagnosable or categorized are classified as Idiopathic MR. This study was carried out to identify the presence of any structural chromosomal aberration in 11 patients, manifested with varying degree of Idiopathic MR. Pedigree analysis of patients' family, GTG banding, HRB and Karyotyping was performed. Evidence of familial origin with visible chromosomal aberration was observed. Genotype-phenotype co-relation could be established only for patients who manifested structural chromosomal aberration, but for others it still remains idiopathic. A detailed molecular genetic analysis like FISH, etc was the need of the hour as MR is Multifactorial and could be attributed to other genetic, epigenetic or environmental factors.