Primary osteoarthritis (OA) is a multifactorial disease with several genetics factors involved. The COL2A1 gene is of particular interest because it encodes for the most abundant protein in articular cartilage. The aim was to evaluate the association of COL2A1 gene polymorphism with OA of the knee in Mexican Mestizo patients. A case-control study was conducted; cases comprised patients with a radiologic scoring > or = 2 and controls with a radiologic scoring <2. DNA was extracted from a peripheral blood sample, the polymorphic site of the COL2A1 gene was submitted to polymerase chain reaction (PCR), and the products were digested using PvuII restriction enzyme. For statistical analysis, a non-conditional logistic regression was developed. There were no associations among alleles in the overall sample, nevertheless, a significant association was found with p (Pp/pp) allele and OA of the knee grade 4 [odds ratio (OR), 95% confidence interval (CI 95%) 4.1 (1.2-14.6)] adjusted by gender, age, and body mass index (BMI). These results suggest an association of a COL2A1 gene polymorphism with advanced stages of OA of the knee in Mexican Mestizo population.