Elachista tengstromi is a moth of the Elachistidae family. It is found from Fennoscandia to Switzerland and Austria, and from Great Britain to Poland. It is also found in Japan. It was formerly considered to be a form of Elachista regificella. The wingspan is 7–9.3 millimetres (0.28–0.37 in). The larvae feed on Luzula pilosa. They form a strongly contracted upper-surface tentiform mine, generally in the lower third of the leaf, beginning at the leaf base. Mostly, a second or third mine is made which starts at the leaf tip. Pupation takes place outside of the mine.