There is growing evidence that social media addiction is an evolving problem, particularly among adolescents. However, the absence of an instrument measuring social media addiction hinders further development of the research field. The present study, therefore, aimed to test the reliability and validity of a short and easy to administer Social Media Disorder (SMD) Scale that contains a clear diagnostic cut-off point to distinguish between disordered (i.e. addicted) and high-engaging non-disordered social media users. Three online surveys were conducted among a total of 2198 Dutch adolescents aged 10 to 17. The 9-item scale showed solid structural validity, appropriate internal consistency, good convergent and criterion validity, sufficient test-retest reliability, and satisfactory sensitivity and specificity. In sum, this study generated evidence that the short 9-item scale is a psychometrically sound and valid instruments to measure SMD. •The 9-item Social Media Disorder (SMD) Scale is a psychometrically sound instrument.•The development of the 9-item SMD-scale was based on the 9 DSM-5 criteria for IGD.•The 9-item SMD-scale shows appropriate internal consistency and test-retest reliability.•The 9-item SMD-scale demonstrates good convergent and criterion validity.•The 9-item SMD-scale shows adequate sensitivity and good specificity.