PurposeAbnormalities in serum magnesium levels have been seen in obesity and its related diseases. Our aim is to determine the mean magnesium levels in overweight and obese children as compared to the levels in normal weight controls to study its relationship with obesity and overweight. The study was done at a tertiary care hospital.MethodsA case-control study was conducted at the Department of Pediatrics, Combined Military Hospital, Peshawar, over a 12-month period from August 7, 2015 to August 6, 2016. A total of 140 children between 2-14 years of age were included in the study. They were divided into two equal groups of 70 children each. Both of the groups were matched according to their age and sex. Children with a body mass index (BMI) greater than or equal to 85th centile and 95th centile were placed in the overweight and obese category, respectively, and termed as cases while the other 70 children with a BMI greater than or equal to 5th centile but less than 85th centile were categorized as the normal weight group and termed controls. The serum magnesium levels of both case and control groups were calculated.ResultsThe serum magnesium levels were significantly lower in the overweight and obese group (2.08 ± 0.211 mg/dl) as compared to the normal weight group (2.55 ± 0.155 mg/dl, p<0.001). A significantly strong inverse relationship was seen between serum magnesium levels and body mass index.ConclusionMean serum magnesium levels in overweight and obese children are lower than those in normal weight children. Further studies are required to see the effect of supplementation of diet with this essential micronutrient on the weight of children.