Borderline personality disorder (BPD) is characterized by a pervasive instability of interpersonal relationships, affects, self-image, marked impulsivity, dissociation, and paranoia. The cognitive dimension of the disorder has received relatively little attention and is poorly understood. This paper proposes that neurocognitive impairment is a key moderator in the development of BPD and elaborates a possible pathway for the expression of the cognitive domain. Neurocognitive impairment is hypothesized to moderate the relationship between caretaking and insecure disorganized attachment and pathological dissociation in the formation of the disorder contributing to impaired metacognition and a range of cognitive difficulties. The empirical evidence from studies of cognitive processes, brain function, attachment, and dissociation that support this theory are reviewed and discussed. Areas for future research that might verify or refute this theory are suggested.