The study of homesickness after a relocation has become a relevant research topic because of its impact on people’s activities and psychological well-being (Stroebe, Van Vliet, Hewstone, & Willis, 2002). Fisher (1989) claims that homesickness should be investigated within a multi-causal model, in which personality, environmental, and situational factors concur. Multiple place attachment, with reference to both the old and the new place of residence, was found to be a relevant environmental factor in the development of homesickness (Scopelliti & Tiberio, in press). In this study, we also considered the size of the new place of residence, as Bonaiuto and Bonnes (1996) have outlined different peopleenvironment transactions in a mediumsized and a large city. A questionnaire focusing on personality factors (vulnerability to homesickness), attachment to the home-town and to the new place of residence was administered to a sample of 188 non-native university students living in Rome (large city) and Chieti (medium-sized city), and coming from the same geographical areas. A control group of 181 native students (100 in Rome, 81 in Chieti) was also included in the study. We first analysed the dimensional structure of vulnerability to homesickness, attachment to the home-town, and attachment to the new place of residence. The factors Expression of emotion/Seeking social support, Rigidity, and Earlier homesickness experiences emerged with reference to vulnerability to homesickness; the factors Identification, Lack of resources, and Social relations emerged with reference to attachment to the hometown; the factors Opportunities for personal development, Involvement, Affective Bond and Friends and integration emerged with reference to attachment to the new place of residence. Then we considered differences between natives and non-natives, and between nonnative students living in different sized cities. No significant difference between natives and non-natives emerged with regard to vulnerability to homesickness factors, both in Rome and in Chieti. This result showed that we actually measured personality factors, that are not supposed to vary between the two populations. Conversely, a relevant role of town size in non-natives’ residential experience was found: with regard to attachment to the home-town, students living in Chieti showed stronger Social relations than students living in Rome; with regard to attachment to the new place of residence, students living in Rome felt higher Opportunities for personal development, a stronger Affective bond with the city and higher Involvement than students living in Chieti. Finally, we tested a model in which actual homesickness was considered within a multicausal framework. The factors Rigidity and Earlier homesickness experiences, Social relations in the home-town, and Involvement in the new place of residence emerged as significant predictors of homesickness. Theoretical and practical implications in the study and prevention of homesickness are discussed.