Leptospira interrogans is a bacterium that can infect most mammal species. Brown rats are considered to be one of the most important reservoirs of Leptospira because they frequently are infected and live in close proximity to humans. Past studies of prevalence of Leptospira in brown rats indicate that temperature - both high and low - may negatively affect the prevalence rate in rats, so that Leptospira is rare or even absent at temperatures below 7-8 °C. Here we investigated the prevalence of infection in brown rats on the Faroese Islands (mean temperature of 6.5 °C) and did not find any infected animals in a sample of 95 animals. We propose that prevalence rates of Leptospira are very low in rural brown rats in the cooler Scandinavian regions, even though urban/sewer rats might be highly infected in the same regions.