OBJECTIVE: To validate the Social Media Disorder scale in Nigerian adolescents by determining its unidimensional structure, reliability, sensitivity, specificity, and criterion validity. METHODS: A total of 516 and 1213 pre-university students in two universities were randomly recruited and assessed using the 9-item Social Media Scale and the 12-item General Health Questionnaire (in the second survey only). RESULTS: 46.3% and 56.3% of respondents in the first and second surveys met the criteria for social media disorder, respectively. Factor loading of items on the latent factor (addiction) was moderate. The model yielded a fairly acceptable fit in both samples. The averaged measure for intra-class correlation was acceptable (0.612). The internal consistency (Cronbach's alpha) was good (0.713 for sample 1 and 0.724 for sample 2). The test-retest reliability among the 113 respondents was good (r=0.696, p<0.001). The item-total correlations were all significant. Sensitivity of each item ranged from 67.7% (tolerance) to 91.3% (escape); specificity of each item ranged from 41.2% (escape) to 87.6% (displacement). For criterion validity, the total Social Media Disorder scale score correlated with General Health Questionnaire items that assess self-esteem, depression, and mood, as well as the total score. CONCLUSION: The 9-item Social Media Disorder scale is acceptable for screening social media disorder in pre-university students in Nigeria. The high prevalence of social media disorder should be of concern to counsellors, teachers, and mental health practitioners. Strategies for public health education on social media use are needed in Nigeria.