Radmanović was selected by the Seattle SuperSonics as the 12th pick of 2001 NBA draft. Although a consistent contributor throughout his first two seasons, Radmanović became a candidate for the NBA Most Improved Player Award in the 2003–04 season. That season he averaged 12 points and 5.3 rebounds per game mostly as a sixth man. He also established himself as an above average three-point shooter, making around 40% of his attempts, a skill that was rare for a player of his size at the time.