The aim of this paper is to explain the underpricing of IPOs in the Spanish Capital Market. We have tested if the existence of asymmetric information between the agents that participate in the IPO and the institutional lag explain this anomaly. According to the results of the study, underpricing is an informative signal of the companies value that begin to be quoted on the Spanish Stock Market. Furthermore, the greater the ex-ante uncertainty, the greater the underpricing will be. Initial return is also influenced by the course followed by the market index.

Key words: initial public offering (IPO), underpricing, asymmetric infor-mation.
JEL classification: G10, G12, G14, G32.