We identified a novel large insertion/deletion (Indel) polymorphism of 1464 bp localized in intron 18 of the human thyroglobulin gene. Data from sequence showed a high A+T content (62%), two 17-bp long motif repeats, and three different types of 10-bp long palindromic sequences. The comparison between these 1464 bp and sequences deposited in National Center for Biotechnology Information (NCBI)/GenBank database exhibit a nonsignificant degree of homology with any previously described sequences. The long polymerase chain reaction (PCR) method was used to amplify the genomic DNA region containing intron 17/exon 18/intron 18/exon 19/intron 19 by primers situated in the introns 17 and 19. The amplification generates two fragments of 3.5 and 5.0 kb that correspond to the exclusion or inclusion of a 1464-bp segment, respectively. Both variants are thus widely represented in the human population; giving allele frequencies of 0.56 (insertion) and 0.44 (deletion). Finally, the polymorphism was confirmed by sequence analysis of the 5.0- and 3.5-kb amplified fragments.