Common throughout much of England and Wales; rare in Ireland. Widespread in Hampshire and on the Isle of Wight, where reasonably common and probably under-recorded. Wingspan 4.9-6.2 mm. Very similar to
Stigmella catharticella, but whereas the posterior legs in that species carry long hairs on the tibia and have dark spots on the tarsi, in
Ectoedemia septembrella the tibia has shorter spines and the tarsi are unspotted (MBGBI Vol 1). Larva mines leaves of Perforate St John's-wort, over-wintering as a pupa.