Many small island developing states (SIDS) face special disadvantages associated with small size, insularity, remoteness and proneness to natural disasters. These factors render the economies of these states very vulnerable to forces outside their control — a condition which sometimes threatens their very economic viability. The GDP or GNP per capita of these states often conceals this reality. In this paper the major vulnerabilities faced by SIDS are discussed and when possible quantified in the form of an index. An attempt is also made to construct a composite index of vulnerability.