Background: False-positive and false-negative answers to screening questions influence prevalence and incidence estimations for stroke in population studies. Despite frequent use in screening, only a few studies have examined causes and influence of incorrect self-reports. We compared the rates of false-positive and false-negative answers to a single question about prior stroke to those of the Stroke Symptom Questionnaire (SSQ), a newly developed instrument based on 6 symptom questions. Differences in stroke prevalence estimations and risk factors for incorrect reports are described. Methods: The MEMO study (Memory and Morbidity in Augsburg Elderly) examines cognitive function and neurodegenerative diseases in an elderly population (n = 384) in southern Germany. All participants filled in the symptom questionnaire, received a neurological examination and a neuropsychological test battery. Medical records were obtained for event validation of subjects positive on screening and those negative on screening with symptoms suggesting a cerebrovascular event during examination. Results: Prevalence of total stroke was 5.3% using a single screening question and 6.8% using the questionnaire. The false-negative rate was higher for the single-question approach (34.2 versus 10.5%). It was strongly influenced by gender and cognitive function. The questionnaire had a higher false-positive rate than the single question. Based on the results, we established question combinations that best served three different research scenarios (frequency estimation, risk factor analysis, control selection), relevant to stroke research in population studies. Conclusions: A single screening question for stroke in the past with event validation by medical records underestimates stroke frequency in population studies by about 30%. Use of a number of questions for key symptoms combined with a general stroke question, as in the SSQ, improves the completeness of event ascertainment and allows the detection of stroke and transient ischemic attack at the same time.