Idiopathic intracranial hypertension (IIH) is an increasingly prevalent disease, characterised by raised intracranial pressure (ICP). Cognitive impairments have been reported in IIH, however evidence support- ing these deficits are scarce and contributing factors have not been defined. Using a bespoke battery of cognitive tests, we identified multiple domains of deficiency in a case-control prospective study of 66 female adult IIH patients. Attention networks (executive function) and sustained attention were impaired compared to a body mass index and age matched control group of 25 healthy female participants. These deficits were not permanent as participants exhibited improvement in several domains over 12 months which were associated with reduction in ICP. Cognition was evaluated before and after a lumbar puncture, with acute reduction in ICP and noted significant improvement in executive function. The impact of comorbidities was explored, with headache severity during cognitive testing, co-morbid depression and markers of obstructive sleep apnoea adversely associated with cognitive performance. Deficits were also significantly associated with impaired reliability to perform visual field tests, the cornerstone of monitoring vision in IIH. Our findings propose that cognitive impairment should be recognised as a clinical manifestation of IIH and treating comorbidities could improve cognitive performance.livgrech@googlemail.com