Rationale Aspirin has positive and negative effects on a number of age-related chronic conditions and there is uncertainty regarding its role in primary prevention in people aged 70 years and over. Aims To assess whether daily active treatment of 100 mg enteric-coated aspirin will extend the duration of disability-free life in healthy older participants. Design A double-blind, randomized, placebo-controlled primary prevention trial undertaken in Australia and the United States with careful adjudication of endpoints including stroke. Study outcome In Australia 16,703 individuals were recruited through general practices across five states and territories, and in the United States, 2411 participants were recruited through 34 clinical sites across the country. Follow-up of participants will finish at the end of 2017 with average follow-up exceeding 4.25 years per person. Discussion The statistical analysis plan for ASPREE, finalized after closure of recruitment but before the end of patient follow-up, outlines the primary analyses and a range of subgroup and sensitivity analyses. (International Standard Randomized Controlled Trial Number Register ISRCTN83772183 and clinicaltrials.gov Number NCT01038583).