Motor neuron disease (MND) and the behavioural variant of frontotemporal dementia (bvFTD) are thought to be part of a disease spectrum. There is uncertainty about the frequency and characteristics of behavioural changes in MND, and similarly, about a relation between bvFTD and the site of onset of MND. Our aim was to perform a systematic review of the publications on behavioural changes in MND. An extensive search for articles on behavioural changes in MND patients was performed. First, cohort studies of MND patients were reviewed to summarize the prevalence of bvFTD and mild behavioural changes. Secondly, data on bvFTD symptoms (mostly from case reports) of individual MND-bvFTD patients were used to analyse characteristics and pooled prevalences of bvFTD symptoms. In addition, site of onset, survival and demographic variables of MND-bvFTD patients were analysed. Results showed that in cohorts, 8.1% (95% CI 5.6 - 11.5%) of MND patients had bvFTD. In 170 individual patients with MND-bvFTD, perseveration (40%), apathy (29%) and disinhibition (26%) were the most frequently reported behavioural changes; 43% had memory disturbances and bulbar onset was found in 48%. In conclusion, 8% of MND patients have bvFTD, with perseveration being reported most frequently. MND-bvFTD is often accompanied by memory disturbances and is related to bulbar onset.