The cognitive profile of a patient, PM, who had damage to the right basal ganglia as the result of a stroke was investigated. Whilst most cognitive functions were intact, she showed specific neuropsychological deficits, most notably a difficulty in developing, through abstraction of the relevant information, a higher-level rule by which to guide behaviour. The types of rule affected were those based upon an attentional set (attending to a particular dimension of stimulus features, such as 'shape') or a response strategy (continuing to apply a previously successful pattern of responses). The learning of lower-level rules based on stimulus-reward values was spared, as was the ability to apply an instructed rule and to discontinue use of rules which were no longer appropriate. These data provide evidence for the dissociability of cognitive functions within the basal ganglia.