Larvae and pupae of Potamyia phaidraMalicky and Chantaramongkol (Trichoptera:
Hydropsychidae) were collected from montane streams in southern Thailand. Pupal identifications
were based on genitalic features in common with described adults, and larvae were associated with
the pupae. Herein, the final larval instar and pupa are described, diagnosed, and figured.