With the introduction of array comparative genomic hybridization (CGH), genome-wide high resolution analysis for DNA copy number alterations became feasible. This technology has been principally used in patients with mental retardation. Depending on the eligibility criteria and resolution of the array, around 10 % of patients with mental retardation are found with cryptic chromosomal imbalance. This figure arises 20 % for patients with mental retardation and multiple congenital anomalies. Alteration of the lipid metabolism and/or regulation of satiety, obesity (except in presence of other "exogen" factors) can be considered as a developmental disorder. Also, different syndromes with obesity have been associated with chromosomal abnormalities, such as 1p36 deletion syndrome, 2q37 deletion syndrome, chromosome 14 maternal disomy … So we can expect that syndromic obesity is similarly associated with sub cryptic chromosomal abnormalities. Some "isolated" patients with obesity have been described with cryptic chromosomal imbalance found by array CGH, but no study has been realized in cohorts of patients selected for syndromic obesity.