We describe a 57-year-old man (MW) with frontal variant frontotemporal dementia (fv-FTD) who presented with a long history of drinking problem and marital disharmony followed by gradual changes in personality with disinhibition, stereotypic checking, overeating and a decline in self-care. Structural MRI imaging confirmed marked frontal atrophy involving particularly the ventromedial region. Performance on standard tests of frontal executive function was largely unremarkable and MW obtained a perfect score on the Mini-Mental State Examination (MMSE). In contrast, an experimental battery of tasks designed to evaluate theory of mind (ToM) revealed marked deficits. MW's challenging and disruptive behaviours, notably obsessive checking of car suspension by rocking, and wandering, responded to behavioural modification regimes adapted from the neurorehabilitation literature. In conclusion, deficits in ToM may underline the gross abnormalities in social conduct, which characterise fv-FTD; ToM appears to dissociate from frontal executive function; and behavioural modification approaches can be of benefit in this disorder.