Trachoma is a major cause of blindness in the developing world and 63 million people are currently infected. Large-scale control programmes are being implemented to clear ocular Chlamydia trachomatis infection--the causative agent of trachoma--and improve environmental conditions to reduce transmission. Chemotherapeutic intervention involves antibiotic administration and the effectiveness of this treatment is currently under investigation. A mathematical model has been developed to allow the impact of control programmes on infection and blinding disease sequelae to be predicted. The model has a structure that allows an important aspect of trachoma pathogenesis to be taken into account, namely the effect of repeated cycles of infection and recovery leading to scarring and the damaging disease sequelae. This novel model structure reproduces many age- and time-dependent epidemiological patterns observed in endemic settings and allows the dynamic effect of treatment on infection and disease sequelae to be gauged.