This study examined whether the Single-Item Math Anxiety Scale (SIMA), based on the item suggested by Ashcraft, provided valid and reliable scores of mathematical anxiety. A large sample of university students (n = 279) was administered the SIMA and the 25-item Shortened Math Anxiety Rating Scale (sMARS) to evaluate the relation between the scores of the two measures. The university students were also administered other tests to provide validity evidence for the SIMA scores. The temporal stability of the SIMA scores was also evaluated over a 7-week test-retest interval. The findings of the study demonstrated that the SIMA scores showed evidence of validity and strong test-retest reliability. We advocate for the use of the SIMA as a quick and useful means of assessing math anxiety, particularly in research and educational settings when large samples have to be assessed.