Over the last decade, the detection of chromosomal abnormalities has shifted from conventional karyotyping under a light microscope to molecular detection using microarrays. The latter technology identified copy number variation as a major source of variation in the human genome; moreover, copy number variants were found responsible for 10-20% of cases of intellectual disability. Recent technological advances in microarray technology have also enabled the detection of very small local chromosomal rearrangements, sometimes affecting the function of only a single gene. Here, we illustrate how high resolution microarray analysis has led to increased insights into the contribution of specific genes in disease.