The Wender-Utah Rating Scale (WURS) is a widely used self-report instrument for retrospective assessment of childhood ADHD. However, many WURS items are not specific to ADHD. Here, we investigated the effect of excluding these items on the performance of the WURS in predicting adult ADHD based on previous diagnosis and current clinically significant symptoms. The study was conducted on a sample of adults (n = 1014; 48 % male) participating in a family-based investigation of ADHD. Participants completed the 61-item WURS questionnaire and the 66-item Conners Adult ADHD Rating Scale. Receiver operating characteristic (ROC) curves were used to compare the performance of the eight-item WURS (WURS-8) and the longer WURS-25 in predicting previous ADHD diagnosis and current clinically significant ADHD symptoms. WURS-8 and WURS-25 have approximately the same power to predict adult ADHD, based on either previous diagnosis or current symptoms (area under the ROC curves >0.8). WURS-8 performs at least as well as the longer WURS-25 in predicting adult ADHD. This 8-item questionnaire is thus a valid instrument and is especially useful for screening for ADHD in large epidemiological samples.