Analysis of tropical nights on the Atlantic coast of the Iberian peninsula. A proposed methodology. This paper presents a new methodology for the study of warm nights, also called «tropical», in Galicia and Portugal in order to identify those nights where people can be affected by heat stress. The use of two indicators obtained through half-hourly data has allowed us to define in more detail the thermal characteristics of the nights between May and October, thereby being able to more accurately assess the risk to the health and well-being of the population. There is a significant increase in the frequency of tropical nights and warm nights on the Atlantic coast, from the north of Galicia to the south of Portugal. The lower latitude and proximity to the coastline are associated with greater persistence of heat and thermal stress during these nights. In inland areas the persistence is less. The warmest nights are more frequent and intense in centres of the cities, due to the effect of the urban heat island.