In the latest (fifth) edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), Internet Gaming Disorder (IGD) was included as a tentative disorder worthy of future research. Since then, several psychometric instruments to assess IGD have emerged in the literature, including the nine-item Internet Gaming Disorder Scale–Short-Form (IGDS9-SF), the most brief tool available to date. Research on the effects of IGD in Portugal has been minimal and may be due to the lack of a psychometrically validated tool to assess this construct within this particular cultural background. Therefore, the aim of the present study was to develop and examine the psychometric properties of the Portuguese IGDS9-SF. A total of 509 adolescents were recruited to the present study. Construct validity of the IGDS9-SF was assessed in two ways. First, confirmatory factor analysis was performed to investigate the factorial structure of the IGDS9-SF in the sample, and the unidimensional structure of the IGDS9-SF fitted the data well. Second, nomological validation of the IGDS9-SF was carried out and the nomological network analyzed was replicated as expected, further supporting the construct validity of the IGDS9-SF. Criterion validity of the IGDS9-SF was also established using key criterion variables. Finally, the IGDS9-SF also showed satisfactory levels of reliability using several indicators of internal consistency. Based on the results found, the IGDS9-SF appears to be a valid and reliable instrument to assess IGD among Portuguese adolescents and further research on IGD in Portugal is warranted.