Social rejection sensitivity has been proposed as a central risk factor for depression. Yet its assessment has typically been limited to offline contexts. Many of today’s social interactions, however, take place online. The aim of the current study therefore was to develop a measure to assess social rejection sensitivity in both online and offline environments. Across four separate samples including a total of 2381 individuals (12-89 years), the Online and Offline Social Sensitivity Scale was shown to offer a reliable measure of social rejection sensitivity. The study provides preliminary evidence that rejection sensitivity across online and offline social environments shows a strong association with depressive symptoms as well as maladaptive ruminative brooding. The study also showed age-related differences in social rejection sensitivity in online and offline contexts with rejection sensitivity decreasing from early adolescence to older age. The scale has the potential to advance future research aimed at understanding the role of social rejection sensitivity in mental health in a digital age.