Posterior tibial tendon is particularly vulnerable and is responsible for much morbidity in sportspersons. Some patients have a predisposition without a clinically recognized cause, suggesting that individual characteristics, inclusive genetic inheritance, play an important role in tendinopathy. Matrix metalloproteinase (MMP)-8 is a proteinase capable of degrading a large amount of extracellular proteins, and influence degradation and remodeling of collagen. To determine whether the −799 polymorphism in the promoter of MMP-8 gene is associated with tendinopathy in posterior tibial tendon, 50 patients undergoing surgical procedures and anatomopathological diagnosis of degenerative lesions of the posterior tibial tendon and 100 control patients with posterior tibial tendon integrity and without signs of degeneration in magnetic resonance imaging were evaluated for the −799 MMP-8 polymorphism. There was a significant difference in the presence of the different alleles (P = 0.001) and genotype (P = 0.003) between the control group and the test group for the MMP-8 gene. The polymorphism at position −799 of the gene for MMP-8 is associated with tendinopathy primary posterior tibial tendon in the population studied. The results suggest that individuals with the T allele are at greater risk of developing tendinopathy.