Aim: To describe associations of abnormalities in the electroencephalogram (EEG) with the most prevalent diagnoses in a memory clinic cohort. Methods: Associations between visual EEG findings and diagnoses in 1,116 consecutive patients [382 Alzheimer’s disease (AD), 274 subjective complaints, 190 mild cognitive impairment (MCI), 118 psychiatric disorder, 61 frontotemporal lobar degeneration, 53 vascular dementia (VaD), 38 dementia with Lewy bodies (DLB)] were determined by prevalence ratio (PR). Results: Diagnoses of subjective complaints [PR = 1.6; 95% confidence interval (CI) = 1.4–1.9] and psychiatric disorder (1.4; 95% CI = 1.1–1.9) were associated with a normal EEG, while subjects with both focal and diffuse EEG disturbances were more likely to have DLB (3.5; 95% CI = 2.1–5.6), VaD (2.3; 95% CI = 1.4–3.6) or AD (1.5; 95% CI = 1.3–1.8). Subjects with only diffuse EEG abnormalities were more likely to have AD (PR = 1.5; 95% CI = 1.3–1.9). The prevalence of MCI was higher among those with only focal EEG abnormalities (PR = 1.3; 95% CI = 1.0–1.7). Conclusions: A normal EEG argues for subjective complaints or psychiatric diagnosis. An EEG with only focal abnormalities supports MCI. An EEG with only diffuse abnormalities argues for AD. An EEG with both focal and diffuse abnormalities argues for DLB, VaD or AD.