Objectives: The purpose of this study is to examine factors related to the delayed arrival of appointment time for outpatients of a psychiatric department in an academic medical center in Korea. Methods: This study investigated relationships of delayed arrival with demographic, appointment related, and practice related factors, by analyzing data related to outpatient appointments for about two years from November 1 in 2013 to October 30 in 2014 at a university hospital in Seoul. Results: Among 95,470 final research subjects, 80,871 outpatients arrival in their appointment time, 14,559 outpatients were late, thus, a rate of delayed arrival is 15.29%. As the results of multiple logistic regression analysis, the odds ratios of delayed arrival become greater as they are younger, male , living in the residence, In-cheon and Gyeong-gi area, and their health insurance types are industrial accident compensation insurance and car insurance. Also, the odds ratios of delayed arrival become greater as the appointment time is from 8:30 to 11:00, they appoint in December, January, and February, and temperature gap is over -2 degrees Celsius between the reserved day and average temperature. Similarly, the odds ratio of delayed arrival is higher as return patients, obsessive-compulsive disorder, and practice by doctor B. Conclusions: This study found that various factor influence delayed arrival of appointment time. Medical institutions should find various methods such as focusing continuously on patients who tend to late their arrival time, developing specific appointment system regulating the factors of delayed arrival, and developing guidelines of the patients who tend to late their arrival time.