Norway is one of the countries that constructs the most road tunnels, and there are well over 1,000 in the country. The aim of the study is to map the prevalence and describe the characteristics of vehicle fires in Norwegian road tunnels 2008-2011. The average number of fires in Norwegian road tunnels is 21.25 per year per 1,000 tunnels, and the average number of smoke without fire is 12.5 per year per 1,000 tunnels. The fires and the instances of smoke without fire do usually not involve harm to people or the tunnels. Of the 135 fires and instances of smoke without fire, we know that 8 involved minor injury to people and that 3 involved serious personal injury and 5 involved death. The present study provides two important findings. The first is the fact that the causes of fires in heavy and light vehicles are different. Technical problems are the most frequent cause of fires and instances of smoke without fire in heavy vehicles, while single vehicle and collisions are the most frequent cause of fires in vehicles weighing less than 3.5 tonnes. The second important finding of the study is that undersea tunnels are substantially overrepresented in the statistics of fires in Norwegian road tunnels. There are 31 undersea road tunnels in Norway. These have a high gradient, defined as over 5 %. In addition, there are 10 tunnels that are not underwater, but still have a high gradient. These 41 road tunnels, which together constitute 4% of road tunnels in Norway, had 44% of the fires and the instances of smoke without fire in the period 2008-2011. Heavy vehicles were overrepresented in these fires, and technical problems were the most frequent cause.