Background and objectives: Admission to university is an important event in the life of youth in every country. Homesickness is one of the most significant issues faced by university students during their education life. The present study aimed to determine the association between homesickness, happiness and the related factors in the dormitory students in Hamadan University of Medical Sciences, Iran. Methods: This cross-sectional, descriptive-analytical study was conducted on 387 dormitory students at Hamedan University of Medical Sciences in Hamedan, Iran during February-March 2015. Subjects were selected via stratified random sampling with proportional allocation. Data were collected using self-report and using demographic and contextual questionnaires, Fenfelit homesickness questionnaire, and oxford happiness questionnaire. Data analysis was performed in SPSS version 23 using Pearson’ s correlation-coefficient and general linear model (GLM) at the significance level of 0. 05. Results: The mean score of homesickness in both genders had a significant difference (P=0. 009). In addition, the mean score of happiness differed in terms of economic status. Homesickness was negatively correlated with the happiness score, so that increased homesickness was associated with reduced happiness. Variables of homesickness, age, internet use, maternal education, health status, economic status, and education level could significantly predict happiness. Conclusion: Mental health of students in dormitories is of paramount importance. Therefore, interventions and preventive programs must recognize the causes of happiness, and appropriate interventions should be developed and implemented based on the influential factors in this regard.