We sought to investigate the association of IL-18 gene variants with measures of obesity and the metabolic syndrome in different age ranges; in healthy children who participated in the Gene – Diet Attica Investigation on childhood obesity (GENDAI) (aged 10–14 years) and a group of healthy women from the Greek Obese Women study (GrOW) (aged 18–74 years). Here, IL18 is linked to obesity due to melanocortin 4 receptor deficiency.