Objective: To explore sleep quality and daytime sleepiness problems in medical students at Ramathibodi Hospital. Methods: This was a cross-sectional study. Data were collected using questionnaires. The questionnaires included (1) Demographic and personal data, (2) The Pittsburgh Sleep Quality Index (PSQI) for sleep quality problem assessment and (3) The Epworth Sleepiness Scale (ESS) for daytime sleepiness assessment. Results: Of 691 medical students, 165 (23.9%) completed questionnaires. The prevalence of poor sleep quality and daytime sleepiness were 63.6% and 41.8%, respectively. After adjusted for age and relationship concern, academic concern (prevalence ratio 1.46) and nighttime activity without screen (prevalence ratio 1.43) were associated significantly with sleep quality problem. No factor was associated with daytime sleepiness. Discussion: Interventions to reduce academic burdens should be promoted to improve sleep problems in medical students. Further studies in larger groups of medical students using both subjective and objective measurements should be done in the future.