Interleukin-10 plays an important role in modulating inflammation and antimicrobial defences. In animal models for bacterial corneal ulcers, high IL-10 levels were associated with a better clinical outcome. We investigated whether IL-10 promotor haplotypes, known to determine IL-10 expression in vitro, are associated with susceptibility to and/or clinical outcome of bacterial corneal ulcers in patients. IL-10 promotor polymorphisms C-819T, G-1082A, A-2763C, and A-2849G for 83 patients with bacterial corneal ulcers and 115 healthy controls were determined by restriction fragment length PCR analysis. For 63 patients and all healthy controls the most frequently occurring IL-10 promotor haplotypes were inferred from these data using the program SNPHAP. A significant underrepresentation of the A-2849A genotype was observed in patients as compared to healthy controls. Both the -2763A allele and the IL-10.1 promotor haplotype were associated with a poor clinical outcome, whereas a favourable clinical outcome was seen in patients carrying the IL-10.2 promotor haplotype. Together, IL-10 promotor haplotypes associated with low IL-10 levels seem to protect against the onset of bacterial corneal ulcers. Once a corneal ulcer has developed, patients carrying IL-10 haplotypes associated with a high IL-10 expression may have a favourable outcome.