Mathias David Grönberg (born 12 March 1970) is a Swedish professional golfer who has played on the European Tour, PGA Tour, and their second-tier tours.
Grönberg was born in Stockholm, Sweden. He won the Swedish Boys Championship in 1988 and the British Youths Championship in 1990. That year he helped Sweden to win the Eisenhower Trophy, and picked up the individual title at that event.
Grönberg turned professional late in 1990. After starting out on the second tier Challenge Tour, he was a member of the European Tour from 1994 to 2003, winning four European Tour events in that time. His best finish on the European Tour Order of Merit was tenth in 1998. However, he was keen to join the PGA Tour in America, repeatedly entering its Qualifying Tournament. After six failed attempts he topped the event in 2003. He had difficulty settling on the PGA Tour, and after his 2005 second season he had to return to the Qualifying Tournament to retain his card, which he did. His best finish in a tour event so far is a tie for 3rd place at the 2007 Valero Texas Open, where he ultimately trailed winner Justin Leonard by three shots.