The Same-day bidirectional endoscopy (BDE) is commonly used in clinical practice. However, the optimal sequence of performing a same-day BDE has not been well-established.The primary aims of this study are to compare the sedative doses and patient discomfort between the study groups who received a colonoscopy followed by and EGD (colonoscopy-EGD), or an EGD followed by a colonoscopy (EGD-colonoscopy) during a same-day BDE. The secondary aim is to assess colonoscopy performance, including the cecal intubation time and adenoma detection rate between the two endoscopic sequences.