This article evaluates whether providing hypothetical or realistic information influences the assessment of decision-making capacity in elderly patients with (and without) cognitive impairment. Decision-making capacity was assessed by means of a clinical vignette that presented a choice about whether to undergo an endoscopic procedure. The following standards of decision-making capacity were evaluated quantitatively and qualitatively: ability to evidence a choice, to understand, to reason, and to appreciate a situation. The vignette was presented to patients in either a hypothetical or real situation. In the hypothetical situation cognitively impaired patients performed significantly poorer than cognitively non-impaired patients on all abilities associated with decision-making capacity (with the exception of evidencing a choice). The realistic situation showed the same pattern among cognitively impaired and non-impaired patients in their ability to understand and in the total vignette score. Both types of patients reasoned about and appreciated the realistic situation equally well. Qualitative analysis revealed that patients gave comparable answers in both hypothetical and realistic situations. The answers were not related to standards of decision-making capacity. Moreover, personal circumstances were taken as a reference point for making a decision, regardless of the situation. We did not find any major differences between the hypothetical and realistic situation. Our findings do raise questions about the validity of hypothetical vignettes, however, especially when used with cognitively impaired persons.