BACKGROUND: Left heart catheterisation with coronary angiography (CA) may lead to cognitive dysfunction, as a result of neurological injury. The aim was to assess the incidence of cognitive dysfunction in elderly patients three months after CA and investigate any association between cognitive dysfunction and microembolic count during CA. METHODS: This was a prospective observational study with a control cohort. Cognitive testing was undertaken at baseline and at 3 months using a battery of 8 neuropsychological tests. Subjects comprised 51 CA patients, aged >/= 50 years, with normal baseline cognition, and 31 community control participants. Microemboli were measured by Transcranial Doppler throughout the procedure. All patients underwent trans-femoral CA with aortography and ventriculography. Cognitive dysfunction was defined in an individual when their reliable change index score was less than -1.96 on 2 or more tests and/or their combined z score was less than -1.96. Microembolic count was assessed by off-line manual counting and automatic software was also used to count and differentiate gaseous from solid microemboli. RESULTS: Cognitive dysfunction was identified in 15.7 of patients at 3 months. Microemboli were detected in all patients, predominantly during aortography and ventriculography. The median total embolic count was 365 (IQR 192, 574), the majority being gaseous (84 ). There was no multivariable association between cognitive dysfunction at 3 months and microembolic count. CONCLUSIONS: This study demonstrated that cognitive dysfunction following CA is not associated with microembolic load. Cognitive dysfunction occurs in 15.7 of patients at 3 months. This is reassuring for the proceduralist and suggests that other perioperative elements are involved.