Cognitive and affective complaints are common in patients with primary hyperparathyroidism (PHPT), but few studies have used psychometric testing to document these symptoms and their response to parathyroidectomy. The current study sought to clarify the nature of cognitive and affective impairments in PHPT and changes postparathyroidectomy. One hundred eleven patients with PHPT underwent neuropsychological evaluation prior to parathyroidectomy with 68 returning for an early postsurgical evaluation. Changes in cognition were assessed using practice effect corrected reliable change indices. Biochemical and anesthesia variables were compared between groups who improved and declined. In a subset of patients, assessment revealed a significant pattern of cognitive slowing, reductions in psychomotor speed, memory impairment, and depression prior to parathyroidectomy. Postsurgical evaluations revealed a trend for improvements on timed tests and depression but a decline in memory. Older patients responded less well to surgical intervention, as did patients who experienced more dramatic changes in biochemical status following surgery. Cognitive changes early postparathyroidectomy are characterized by improved information processing speed and decline in verbal memory, with younger patients more likely to recover during this acute phase. The need for longer-term follow-up studies and increasing utilization of neuropsychological assessments in this population are discussed. (JINS, 2009, 15, 1002–1011.)