OBJECTIVE: To investigate the association between the mannose binding lectin gene (MBL) promoter and structural single nucleotide polymorphisms (SNP) with development of erosions in a primary care inception cohort of patients with inflammatory polyarthritis (IP). METHODS: DNA was available from 438 patients with IP and radiographic data were available for all patients at 5 years. Four SNP [MBL-550*C/G (H/L), MBL-221*G/C (Y/X), MBL codon 52*C/T, and MBL codon 54*G/A] mapping to the MBL gene were genotyped using primer extension techniques. Allele frequencies were compared between IP cases with erosions by 5 years and those without. RESULTS: None of the SNP were associated with erosive outcomes by 5 years. Furthermore there was no association with Larsen score by 1 or 5 years or with the change in Larsen score between 1 and 5 years. Similarly, the genotype combinations known to encode for low MBL protein production were not associated with erosive outcome in the IP cohort as a whole or in those with rheumatoid arthritis (RA) by 5 years. CONCLUSION: Polymorphism within the MBL gene is not associated with presence or extent of erosions by 5 years in patients with RA or IP