The 1998–99 Iowa State Cyclones men's basketball team represents Iowa State University during the 1998–99 NCAA Division I men's basketball season. The Cyclones were coached by Larry Eustachy, who was in his 1st season. They played their home games at Hilton Coliseum in Ames, Iowa and competed in the Big 12 Conference. At the conclusion of the season Head Coach Tim Floyd accepted the same position with the Chicago Bulls of the NBA. Iowa State hired Utah State Head Coach Larry Eustachy to replace him.