Objective: Description of the neurocognitive/neurobehavioral syndrome and prognosis following vertebral artery aneurysm. Method: Two case studies of vertebral aneurysm are presented, one due to serial CVA and the other being a cerebrovascular complication of chiropractic manipulative error. In the first case, a series of cerebrovascular events affected both vertebral arteries, while in the second case both arteries were damaged at the same time. In both cases, blood flow through the damaged arteries was markedly reduced but not eliminated. Consequently function was partially preserved in situations of low to moderate task demand for the affected substrate while it was dramatically reduced in situations of high demand. Because the damage differentially affected the right cerebral hemisphere in both cases, each survivor was susceptible to sudden-onset moods of hypomanic-like affect, and these moods appeared to induce state dependent learning. Thus insight was greater during periods of normal mood than periods of expansive mood, while recall of extra-personal information was greater within than across these mood states. Results: Problems of fluid intelligence (selective and divided attention, new learning, and executive function) were inconsistent across situations and over time, being most extreme under high task demand during the expansive mood state. Both survivors were injured by impulsive actions taken during the expansive mood states. Adaptation to disability was substantially limited by the inconsistency of insight. Social and familial relationships were partially disabled during the expansive mood states. The inconsistency of metacognitive awareness of deficit and compliance with restrictions and limitations during the expansive mood states made treatment and caregiver supervision ineffectual. In the first case, the survivor expired after a series of cerebrovascular events, while in the second instance the treating physician prescribed antidepressant medication which exacerbated the expansive states and led to multiple fugue states. Conclusion: Because the effects of this unusual neuropathology are so specific, unique, and resistant to conventional modes of intervention, treatment should be supervised by specialists in neuropsychology and neurology, and management on an outpatient basis is likely to be both problematical and ineffective. The sequela of state-dependent learning requires in-depth investigation and innovative intervention.