 He won the 1977 North America championships in Vancouver, British Columbia, Canada, and competed a week later at the 1977 Mr. Universe in Nîmes, France, placing second to Kal Szkalak.In 1978, Mentzer won the Mr. Universe in Acapulco, Mexico with the first and only perfect 300 score.He became a professional bodybuilder after that 1978 Universe win.