Psychopathy was one of the most common diagnoses in Finnish forensic psychiatric examinations between the 1910s and 1960s. Abnormal categories of emotions such as sensitivity, indifference and the tendency to shift among different emotions or lability, were among the principal symptoms of psychopathy. This paper describes and analyses the ways in which Finnish forensic psychiatrists between the 1900s and 1930s perceived and portrayed the emotions of individuals they considered to be psychopaths, and how abnormal categories of emotions persisted until the end of the 1960s. Psychopathic categories of emotions were defined along a spectrum ranging between the extremes of sensitivity and of coldness and included volatility, which entailed rapid mood swings. Displaying either or both extremes of emotion defined psychopathy. The unifying category of abnormal emotions disappeared when the diagnosis of psychopathy ceased to exist in 1969, when it was replaced by the diagnostic category of personality disorders.