Distribution and habitat description of the endangered Junín Rail Laterallus tuerosi were assessed during a field study between 6 and 20 February 2014 in the marshes surrounding Lake Junín in the high Andes of Peru, which is the only known locality for the species. By using point counts and playback, we found the species to be present in the marshland all around the lake, with preference for two clearly defined habitat types: one comprising extensively grazed tussocks of Festuca dolichophylla and the other of rather uniform stands of Juncus balticus with undergrowth, or smaller open spaces, with various low herbs. We estimate the suitable habitat of the species to be a minimum of 100 km² and based upon our point count data we provide indicative population figures of 6,200 individuals, which is higher than previous estimates. No records were obtained without playback, although five minutes of silent listening prior to playback were used at each point. All records were in vegetation of at least 0.5 m tall and in the marshy edge on muddy ground with less than 20 cm of water depth. Grazing especially by sheep or cattle is a serious threat to the marsh vegetation structure essential for Junín Rail and the rail is also under pressure from fluctuations in water levels accentuated by regulation for hydroelectric power.