Background: The post-IPO anomalous behaviour in the short and long-run are among the well-recognised anomalies in corporate finance, and exist on all equity markets. The researchers are not unanimous what causes these phenomena’s, and previous research has primarily focused on the US and European markets. Purpose: The study aims to investigate the market performance of Swedish IPO's in the short- and long-run in-between 2007-2017 for different sectors. Method: The market adjusted initial return method was used to calculate the short-run initial return. The Even-time approach with the Buy-and-hold methodology was used to calculate the long-run abnormal returns. A regression analysis was adopted to investigate the relationship between some existing theories for explaining underpricing. Conclusion: Overall the sample set for the study were on average underpriced with 9,25 %, furthermore, no evidence was found that Swedish IPO’s underperformed in a three-year period compared to the market. Of the theories tested, the signalling hypothesis was significant and can be one determinant for underpricing of Swedish IPO’s.