This study contrasts the performance of a 17-year-old female subject with Turner's syndrome before and after developing left temporal lobe seizures, as a means of identifying the mechanism responsible for the Turner's syndrome spatial impairment. The results revealed a deficit in spatial processing before onset of the seizure disorder. Results also revealed that, after developing the seizure disorder, the subject exhibited a selective verbal recall deficit, a marked improvement in spatial cognitive functioning, and a slight shift towards greater right hemisphere involvement in nonverbal processing. These findings may reflect an interaction between the specific neurological functioning of the patient and the resulting left hemisphere dysfunction from the seizure disorder. The mechanism responsible for the spatial disorder in Turner's syndrome might be one of inappropriate hemisphere activation due to inhibition by the left hemisphere over the right. Includes 45 references. (JDD)