We are going to explain a case of a patient diagnosed with psychopathy and his twin brother with a normal personality.

To show the controversia about psychopathy and twins.

Description of a case of psycopathy. We evaluated his psychopatology using the Psychopaty Checklist (PCL).

A 18-years-old male teenager admitted to a penitentiary facility for several crimes: drug dealing, violent theft and multiple aggressions.

Personal history: early psychological and psychiatric attention for disruptive behaviour as a child: repeated lies, low empathy, defiance to parents and teachers, indifference to punishment, robbery, aggressive behaviour, loitering, escaping from home, cruelty against animals, promiscuity, vandalism and drug abuse. Medium-high class family, well-structured family, none of them with criminal history or mental disorders, his brother is a brilliant student.

Personality assessment: We describe 20 features of his personality according to the PCL and we score them from 0 to 2. Zero if it does not apply at all, one if there is a partial match, two if there is a good match.

Features: Superficial charm, narcicism, pathological liar, manipulator, absence of guilt, superficial affection, absence of empathy, inability to accept responsibility, need for constant excitation, parasitic life, unrealistic goals, impulsivity, irresponsibility, low self-control, conductual problems since childhood, juvenile delinquency, repeal of conditional freedom, criminal versatility, promiscuity and multiple marriages.

Out of a maximum score of 40, the cut-off for psychopathy is 30.

This patient has 34 points so we can conclude he is a psychopath.

We can conclude there is not a clear relationship between twins and psychopathy.

The authors have not supplied their declaration of competing interest.