He won the first of his six World Championship gold medals in 1994 at the age of 20 in Mexico City. In 1998, with Maxim Opalev now representing Russia in the C-1 events, Kostoglod teamed up with Aleksandr Kovalyov for the C-2. The pairing was an immediate success, winning two consecutive world 1000 m titles in 1998 and 1999. His other three medals have all come in the C-4 events. Three medals he won at the 2003 championships in Gainesville were stripped from Kostoglod when his teammate Sergey Ulegin tested positive for doping.