The WHO has initiated a program to eliminate blinding trachoma by the year 2020, in large part by mass oral azithromycin distributions. It is not clear how frequently or for how long these treatments are necessary. Here we assess the frequency and duration of treatment.  40 villages in the Gurage Zone of Ethiopia were randomly assigned to biannual treatment, annual treatment, and a single treatment. Each treatment consisted of a single dose of oral azithromycin to the entire population over the age of 1 year (when the study was started, azithromycin had not yet been approved for ages below 1 year). We assess the prevalence the ocular chlamydia that causes trachoma in the peak prevalence age of 1-5 years at baseline, and 2, 6, 12, 18, and 24 months post treatment. An extension of the study monitors infection at 30 and 36 months post treatment. Untreated villages from the same area are enrolled in a step-wedge design to assess the presence of a secular trend. A random sample of those not within the 1-5 year old age group are examined to assess the prevalence of infection in the entire community.