Repetitive negative thinking (RNT) is a key risk and maintenance factor for many psychological disorders and is considered a transdiagnostic process. However, there are few disorder-neutral measures that assess RNT in adults, only 1 of moderate length considered suitable for children, and none that are validated for both children and adults. This study aimed to address this gap by developing a brief measure of RNT that can be used with both children and adults and can be quickly administered in research and clinical contexts. In Study 1, we administered the new 5-item Persistent and Intrusive Negative Thoughts Scale (PINTS) to 527 children (50.3% boys; = 11.2). A 1-factor model fit well and was invariant for boys and girls. The scale showed high internal consistency and good stability across a 2-week interval. The PINTS was significantly associated with measures of depression, anxiety, and disordered eating and was weakly associated with adaptive forms of coping, demonstrating good divergent validity. In Study 2, there were 419 adults (38.9% men; = 31.7) who completed the PINTS. The results replicated and extended the results of Study 1 by demonstrating that the PINTS had good construct, convergent, and criterion validity as well as good internal consistency and stability over time and was invariant across gender and age. It was concluded that the PINTS is a brief, valid, and useful tool for investigating RNT as a transdiagnostic process in the etiology and maintenance of psychological disorders in both children and adults. (PsycINFO Database Record (c) 2019 APA, all rights reserved).