UDN

UDN can stand for:
 * National Democratic Union (Brazil) (União Democrática Nacional),a political party that existed in Brazil between 1945 and 1965
 * Univision Deportes Network, a Spanish-language sports channel in the United States
 * Ulcerative dermal necrosis, a disease of salmon and trout
 * United Daily News, a Taiwanese newspaper
 * IATA airport code for Codroipo civil airport in Italy
 * Unique Device Name of the UPnP Device Architecture
 * Undiagnosed Diseases Network, an NIH-funded study of intractable medical conditions that have eluded diagnosis
 * University of Da Nang, a public university system in Vietnam