The Quick Delay Questionnaire (QDQ) is a self-report measure of delay-related behaviors in adults, and the present study aimed at investigating the psychometric properties of QDQ scores, how well they can discriminate between ADHD adults and both clinical and nonclinical controls, as well as their relations to measures of functional impairments. In the present study, QDQ ratings, a laboratory measure of delay discounting, and ratings of functional impairments were collected from adults diagnosed with attention-deficit/hyperactivity disorder (ADHD; n = 51), a clinical control group with other psychiatric disorders (n = 46), and a nonclinical control group (n = 105). Results showed that the QDQ scores showed adequate reliability. Adults with ADHD had higher scores compared with normal controls on both QDQ subscales, and they also reported higher levels of delay aversion than the clinical controls. Logistic regression analyses showed high specificity but low sensitivity when trying to discriminate between adults with ADHD and nonclinical controls. QDQ scores were not associated with a laboratory measure of delay discounting, but with functional impairments such as substance use, criminality, and money management. Our findings indicate that QDQ scores are reliable, but this instrument should be regarded as a complement rather than as a replacement for laboratory measures. The relatively low sensitivity of QDQ scores is in line with current models of heterogeneity stating that only a subgroup of individuals with ADHD has high levels of delay-related behaviors. Our findings further indicate that this subgroup may be at particularly high risk for problems in everyday life.