Silene longisepala Nasir (Caryophyllaceae) is a plant endemic to Chitral District in mountainous north-west Pakistan. This taxon was previously known from only two localities. In field studies during 2005–2007, 24 new localities in lower Chitral were discovered. We found 608 mature individual plants in 22 localities in 2005, 520 mature individuals in 17 localities in 2006, and 531 mature individuals in 18 localities in 2007. Considering the population size in 2007, an extent of occurrence of 3,587 km2 and area of occupancy of 104 km2, we recommend that the species is categorized as Endangered on the IUCN Red List. The main threat to the species is habitat destruction from road construction, land conversion for agriculture and soil erosion following deforestation; we witnessed the direct effects of these pressures on S. longisepala during our fieldwork. In some localities, however, S. longisepala is fortuitously protected by the general inaccessibility of its habitat. There is no legal framework in Pakistan for the protection of rare and endemic plant taxa on private lands and therefore ex situ conservation may be required for narrow endemics such as S. longisepala. Our methodology in this study, in which we combined detailed field surveys with monitoring, could form a model for conservation research on rare and endemic plant taxa in Pakistan and elsewhere.