Genetic forms of frontotemporal dementia (gFTD) are rare but devastating conditions, with the most prevalent mutations occurring in genes C9ORF72, GRN or MAPT. Clinical manifestations can be highly variable, particularly in those with expansions of the C9ORF72 gene. Crucial to the development and trialling of any novel disease-modifying therapy is the ability to accurately and objectively stage the condition of interest. Defining the clinical stages of FTD is challenging, in particular pinning down the exact point of clinical symptom onset. This impacts our ability to provide accurate prognostic advice to mutation carriers and on clinical trials of novel therapies.