Background: Twitter and WhatsApp may have the potential to negatively affect quality of sleep. Aim of Study: To assess the impact of using social media (i.e., Twitter and WhatsApp) on sleep quality and to identify risk factors associated with poor sleep quality among medical students in King Khalid University (KKU). Methodology: Following a cross -sectional design, 286 medical students at King Khalid College of Medicine, Abha, Saudi Arabia, were recruited into this study. An anonymous self-administered questionnaire has been designed by the researchers which included sociodemographic data, extent of using the WhatsApp and/or Twitter and the Pittsburgh sleep Quality Index. Results: 76.2% of students use both Twitter and WhatsApp, 21.5% use WhatsApp only, 1% use Twitter only, while 1% do not use any. Most medical students (89.8%) use Twitter/WhatsApp every day. Most medical students use Twitter/WhatsApp for 3-4 or more than 5 hours daily (31.1% for both). Most medical students (88.7%) use Twitter/WhatsApp during night. 29.7% of medical students have poor quality of sleep. Twitter/WhatsApp use was significantly more among female than male medical students (81.7% and 73.1%, respectively, p=0.014). Use of Twitter/WhatsApp by medical students differed significantly according to their scholastic year (p=0.014), with highest use among 6 th year medical students (94.1%). Medical students' quality of sleep differed significantly according to their scholastic year (p=0.02), with highest prevalence of poor quality among those at their 2 nd and 6 th scholastic years (37.7%) and 37.3%, respectively). Quality of sleep differed significantly according to students' daily use of Twitter/WhatsApp (p=0.022), with highest prevalence of poor sleep quality among those who spend more than 4 hours daily using Twitter/WhatsApp. Conclusions: The majority of medical students in KKU, especially females and final year students, use Twitter and/or WhatsApp. Almost one third of students have poor sleep quality, especially 2 nd and final year medical students and those who use social media for more than two hours daily. This study indicates a strong need for integrating sleep hygiene education for medical students and to provide health education to promote correct and effective use of social networks.