In foreign literature, the term ‛dyadic death’ is used to describe a situation of a murder followed by the perpetrator’s suicide. It differs from the term ‛extended suicide’ used in Poland. While it is recognized that the occurrence of ‛dyadic death’ can be caused, apart from mental disorders, by unfavorable environmental factors, ‛extended suicide’ is equated with the occurrence of severe depressive disorders in the perpetrator. The above-mentioned constructs describing a homicide-suicide were analyzed from the psychiatric and criminological point of view. The study shall discuss a case of a young woman who drowned her young son in a public place, and then declared her suicide intentions. An analysis of the course of mental disorders in the perpetrator, her biological burdens, situational and family conditions was carried out, and the personality factors that led to her mental decompensation were taken into account. Pathological motivational background of the perpetrator of her son’s murder was clearly modified by her personality dysfunctions exacerbated by life difficulties. It differed from the motivation of a ‛typical’ perpetrator of ‛dyadic death’ or ‛extended suicide’ presented in the literature. Settlements in cases involving murder and subsequent suicide attempts require a thorough forensic-psychiatric and criminological analysis. In some cases, the terms describing such situations do not refer to the clinical condition of the offender but to the nature and image of the crime. Abuse of these terms may contribute to judicial errors.