The present article aims to examine the ways in which social support may affect the adaptation of individuals to a novel social environment. A distinctive feature of this research was the assessment of social support both before and after entering a completely new network of social relationships. A cohort of international exchange high school students (N = 242) was administered a battery of self-report questionnaires dealing with personality traits, perceived social support, coping behaviors and emotional distress before leaving Japan and six months after living with a host family in a foreign community. Perceived social support abroad contributed to less emotional distress. This health-promoting effect of social support was found to be mediated by adaptive coping behaviours, and was not due to confounding by personality traits. Perceived social support at home was predictive of more emotional distress abroad. Subjects who reported high levels of social support at home were particularly vulnerable when they entered the completely new environment and found that such support was no longer available.