The Candrive II/Ozcandrive study, a multicentre prospective cohort study examining the predictive validity of tools for assessing fitness to drive, aims to develop an in-office screening tool that will help clinicians identify older drivers who may be unsafe to drive. This paper describes the study protocol. We are following a cohort of drivers aged ≥70 years for up to 4 years. Starting in 2009, 928 participants have been recruited in seven cities in four Canadian provinces, as well as 302 participants in two sites in Melbourne, Australia and Wellington, New Zealand. Participants underwent a comprehensive assessment at baseline and repeat the assessment yearly thereafter, as well as a brief follow-up assessment at 4 and 8 months each year. A recording device is installed in participants’ vehicles to assess driving patterns, and driving records are obtained from licensing authorities to determine the outcomes: at-fault crashes per kilometre driven and violations. To date, the protocol has been generally well adhered to, with 1230 participants, and barriers and challenges are being addressed, as necessary. The Candrive II/Ozcandrive study is unique owing to its size, duration, partnerships with Canadian, Australian and New Zealand stakeholders, and international research collaboration.