HDN may refer to
Medicine Hemolytic disease of the newborn, an alloimmune illness Hydronephrosis, hydrostatic dilation of the kidney
Places Harlesden station, England, station code Yampa Valley Airport, Colorado, US, IATA code
Other Hyperdimension Neptunia, a video game series Hydrodenitrogenation, an industrial chemical process Northern Haida language of North America, ISO 639-3 code Philippine Human Development Network Hdn., an abbreviation for the Greek grammarian Aelius Herodianus