Objectives:
This work aims to present the difficulties in the assessment of sanity of a perpetrator involved in the so-called dyadic death, which in Poland is identified with the occurrence of sever mood disturbances at the time of the crime.

Methods:
Case: A case of a man who killed his wife and two children is presented. The perpetrator himself tried to commit suicide by cutting his veins with a razor.

Conclusions:
Commentary: The authors underline diagnostic difficulties which were encountered in the analysed case, they point out the necessity to go beyond the phenomenological aspect of “dyadic death” and the need for multidimensional clinical evaluation of the perpetrator. The rarity of similar acts and low survival rate of perpetrators leaves experts with relatively small amount of opinion giving experience. Thus, there is a need for high accuracy research and careful consideration.