There are numerous reports of multi-system genetic disorders with obesity. Many have a characteristic presentation and several, an overlapping phenotype indicating the likelihood of a shared common underlying mechanism or pathway. By understanding the genetic causes and functional perturbations of such syndromes we stand to gain tremendous insight into obesogenic pathways. In this review we focus particularly on Bardet-Biedl syndrome, whose molecular genetics and cell biology has been elucidated recently, and Prader-Willi syndrome, the commonest obesity syndrome due to loss of imprinted genes on 15q11-13. We also discuss highlights of other genetic obesity syndromes including Alstrom syndrome, Cohen syndrome, Albright's hereditary osteodystrophy (pseudohypoparathyroidism), Carpenter syndrome, MOMO syndrome, Rubinstein-Taybi syndrome, cases with deletions of 6q16, 1p36, 2q37 and 9q34, maternal uniparental disomy of chromosome 14, fragile X syndrome and Börjeson-Forssman-Lehman syndrome.