In lower animals and humans, stress/anxiety can enhance dorsal striatal-dependent habit memory,at the expense of hippocampal-dependent cognitive memory. The present review considers the potential for this 'stress/anxiety-induced habit bias' to explain some aspects of post-traumatic stress disorder (PTSD). In rats,anxiety induced by peripheral or intra-amygdala infusions of anxiogenic drugs can enhance habit memory and impair cognitive memory. In tasks in which both habit and cognitive memory processes may provide a learned solution, stress and drug-induced anxiety favors the use of habit memory. The effect of stress and anxiety on the use of multiple memory systems in rats depends on the functional integrity of the basolateral amygdala. Thus,under robust emotional arousal, amygdala activation can modulate the relative use of memory systems in a manner that favors habit memory. We propose a similar mechanism may underlie the development and persistence of some PTSD symptoms. The traumatic memories of PTSD patients can be deficient in hippocampus-dependent contextual or autobiographical aspects, and enhanced in responding to trauma-related cues, which we suggest may reflect increased involvement of the dorsal striatum.We briefly consider the potential role of a stress/anxiety induced habit bias with regard to other psychopathologies,including obsessive-compulsive disorder and drug addiction.