Childhood obesity has become a pandemic. Obesity is the mostimportant cause resulting in the development of insulin resistance and itscomplications. Obesity is a central feature of some genetic syndromes. Thisstudy included 18 patients with syndromic obesity (9 cases with Prader Willisyndrome (PWS) and 9 cases with Bardet Biedl syndrome (BBS)) and forcomparison another 19 cases with simple obesity were included in the study.The aim of the work was to study differences in the degree of insulinresistance between patients with syndromic obesity and those with simpleobesity. History, Clinical examination, detailed anthropometricmeasurements and laboratory investigations including Homeostatic ModelAssessment (HOMA) for evaluation of insulin sensitivity were done for allpatients. The results revealed that patients with PWS had lower meanHOMA values when compared to subjects with simple obesity; however thedifferences were statistically insignificant, while patients with BBS showedinsignificant differences regarding HOMA values when compared tosubjects with simple obesity.