Investigated the impact of a congenital prefrontal lesion and its resection on decision making under risk and under ambiguity in a female patient (aged 51 years) with right mediofrontal cortical dysplasia. Both kinds of decision making are normally associated with the medial prefrontal cortex. In addition, the pre- and postsurgical functional magnetic resonance imaging (fMRI) activations when processing information relevant for risky decision making were studied. Pre- and postsurgical neuropsychological performance was assessed by measures of intelligence (Leistungspruefsystem, subtest 'reasoning'), memory (Verbal Learning and Memory Test and Wechsler Memory Scale-Revised), attention (Testbatterie zur Aufmerksamkeitspruefung, TAP), and information processing and executive functions (Trail Making Test, Color Word Inference Test, and Modified Card Sorting Test). Results indicate selective impairments of ambiguous decision making pre- and postsurgically. Decision making under risk was intact. In contrast to healthy subjects, the patient exhibited no activation within the dysplastic anterior cingulate cortex but left-sided orbitofrontal activation on the fMRI task suggesting early reorganization processes.