During the summer of 2018 large parts of Sweden experienced a record-breaking heatwave regarding temperatures and duration. Previous studies from Sweden with less extreme heat have shown that daily mortality is expected to increase during periods with high temperatures. Between the 2nd of July and 5th of August, the period in 2018 with the highest temperatures, 635 more deaths were observed in Sweden compared to the same period in 2017. This corresponds to an 8, 2% increase over the entire heatwave, and a 13, 5% increase during the warmest week, the 16th to 22nd of July. When using temperature data from four weather stations and relative risks from the models established for the Swedish heatwave early warning system, the heat episode in the summer of 2018 could be expected to result in 601-746 excess deaths, depending on model choice. Comparison with the observed mortality data therefore confirm the ability of the risk models to predict the expected increase in mortality also during longer periods with higher temperatures than ever studied before in Sweden.