This study investigates the interaction between firm size and IPO underpricing in the US and Canadian markets between the years 2007-2016. We find a size effect on IPO underpricing in both Canada and the US, which is larger for Canadian firms. Canadian small firms show more underpricing than US small firms (19.32% vs. 13.87%). Large Canadian firms also exhibit more underpricing than their US counterparts over the sample period (12.83% vs. 10.09%). A size effect on performance is not apparent for holding periods beyond six months from the IPO in both countries, consistent with seasoning effects that reduce information asymmetries across firms over longer investment horizons. Keyword: IPO performance; size effects; short-term information asymmetries