The Generalised Anxiety Disorder-7 (GAD-7) is a self-report scale used to assess general anxiety symptoms. Although the GAD-7 has been found to be a valid scale among adults, studies examining its psychometric properties among adolescents in high-income countries are notably limited and particularly non-existent in low- and middle-income countries. The current study addresses this lacuna by investigating the factorial validity, construct validity, internal consistency and discriminant accuracy of the GAD-7. Data were collected from 553 adolescents (boys = 231; average age = 16.85) recruited from a senior high school in Ghana, a sub-Saharan African country, using cross-sectional self-report methodology. The result supports a unidimensional structure of the GAD-7 that was invariant across gender. The GAD-7 correlates significantly with measures of anxiety, suicidal tendencies and mental well-being, suggesting construct validity. The internal consistency of the GAD-7, based on the mean inter-item correlation value of 0.24 and Cronbach’s a = 0.69, is adequate. The GAD-7 similarly discriminated between individuals at high risk of suicidal tendencies and depression from those with low or no risk, with area under curve values of 0.71 and 0.70, respectively. The GAD-7 is a reliable and valid measure to screen for generalised anxiety disorder among adolescents in Ghana.