IntroductionThe degree to which the change of season influences mood, energy, sleep, appetite, food preference,and the wish to socialize has been called “seasonality” [1]. In 1984 Rosenthal and associatesdescribed the syndrome of “seasonal affective disorder” (SAD), a condition where depressions in falland winter alternate with non-depressed periods in the spring and summer [5]. Seasonal AffectiveDisorder (SAD) is supposed to be caused by lack of daylight in winter [6]. Ulaanbaatar city is thecoldest capital in compared with medium temperature of the world. That’s why, it is an idea that wesupposed to there might be a seasonal affective disorder in this city. There is nothing to be studiedbefore related to this topic and that is our goal of the study.GoalTo determine a seasonal affective disorder in the adults of Ulaanbaatar cityMaterials and MethodsIn this study, we examined 560 healthy people between 20-60 aged livings in the Ulaanbaatar cityusing by Seasonal Pattern Assessment Questionnaire.ResultGender distribution showed an increased incidence of females (56.1%, 314 cases) compared withmale (43.9%, 246 cases). Distribution by age groups shows that 20-29 years were 237 (42.3%),30-39 years were 99 (17.6%), 40-49 years were 132 (23.5%), and 50-59 years were 92 (16.4%).According to the Seasonal Pattern Assessment Questionnaire, below 8 score was 323 (57.6%), 9-10 score 53 (9.4%), over the 11 score 184 (33%).ConclusionAccording to the questionnaire of Seasonal pattern assessment, 33 percent were seasonal affectivedisorder. It means Mongolian people of Ulaanbaatar have Seasonal affective disorder.