Maternal filicide is defined as the murder of a child by its mother. Many classifications have been elaborated based on underlying motives such as altruism, mental pathology, fatal maltreatment, spousal revenge, or an unwanted child. Pathological filicide refers to cases in which the perpetrator has a major psychiatric illness. Related literature is sparse. The present work proposes to identify the main characteristics of mentally ill filicidal mothers. This study was based on data gathered through a retrospective chart review of all filicidal women admitted to the Henri Colin secure unit (France) between 1996 and 2019 (N = 17). Most filicidal mothers had a dysfunctional childhood marked by emotional neglect, intrafamilial violence, or social isolation. They were often married, on average about 32 years old. We found a history of attempted filicide in 3 cases, and abuse or neglect in 3 other cases. The victim's average age was 6.2 years old, and in several cases, multiple siblings were murdered. Half of the filicidal mothers had a history of psychiatric disorders. Three different diagnoses were found in our study: bipolar or depressive disorders (41.2%); schizophrenia or other psychotic disorders (41.2%); personality disorders (17.6%). We identified two subgroups, as having different motivational profiles. In the first group, filicide is a defensive reaction to a perceived threat:The murder is committed under the influence of hallucinations or delusions. In the second group, filicide is linked to a context of separation, real or imagined. Several forensic and psychopathologic features associated with each profile are detailed.