Although well-known from head trauma and acute strokes, sociopathic behavior from dementia is less known and understood. This study reviewed 33 dementia patients who had been in trouble with the law. They were divided into two groups: 22 who committed impulsive sociopathic acts and 11 who committed non-impulsive acts. The impulsive patients demonstrated nonviolent acts, such as dis-inhibited sexual behavior or pathological stealing, and had disproportionate frontal-caudate atrophy on neuroimaging. The majority of non-impulsive patients demonstrated agitation-paranoia, sometimes with reactive aggression, delusional beliefs, or aphasic paranoia, and had advanced memory and other cognitive impairment. The impulsive patients tended to have frontally predominant illnesses such as frontotemporal dementia or Huntington’s disease, whereas the non-impulsive group tended to have Alzheimer’s disease or prominent aphasia. Sociopathy has different causes in dementia. Two common mechanisms are disinhibition, with frontally predominant disease, and agitation-paranoia, with greater cognitive impairment. These forms of sociopathy differ significantly from the antisocial/ psychopathic personality.