The human insulin-responsive glucose transporter 4 gene (GLUT4) has been related to non-insulin-dependent diabetes mellitus (NIDDM) in several studies. Obesity is commonly found in patients with NIDDM. Hence, genes involved in NIDDM might also be relevant for obesity. We have analyzed 212 extremely obese children and adolescents, 82 normal-weight students, and 94 underweight students for two single nucleotide polymorphisms (SNPs: promoter -30G/A; exon 4a: silent 2061T/C) in the vicinity of the GLUT4 by polymerase chain reaction with subsequent restriction fragment length polymorphism analyses (PCR-RFLP) or single-strand conformation polymorphism analyses (SSCP). Allele and genotype distributions were similar in all study groups (all p values > 0.05). Hence, we did not detect association of any of the analyzed SNP alleles in the GLUT4 to different weight extremes, so these seem not to be involved in weight regulation in our study groups.