1990

The 15-round series in 1990 saw Wayne Rainey of Team Marlboro Yamaha Roberts take his first-ever GP championship title. Yamaha also won its sixth manufacturer's title in the 500cc class.

Rainey kicked off the season with a pole-to-finish victory in the opening round in Japan. In the following round in the USA, he won the race with a six-second margin over the 2nd-place finished to lead the championship ranking. Moving on to the European rounds, he took four wins, five 2nd-place finishes and one 3rd from the third round in Spain to the 12th round in Sweden. He defended his lead in the ranking to round 13 in Czechoslovakia. Up to this point, Rainey had 220 points and Kevin Schwantz (Suzuki) was behind him in the ranking at 173 points. In this race, Rainey and Wayne Gardner (Honda) battled while Schwantz took a fall in lap three as he chased the duo and was forced to retire from the race. This gave the championship title to Rainey with two races still remaining in the series. It was the first championship for Rainey and came in his third season of full-series GP competition.
Other Yamaha riders also performed well, with Juan Garriga of the Ducados Yamaha Team finishing 6th, Eddie Lawson 7th (affected by missing GPs after a break in his right heel) and Jean-Philippe Ruggia and Christian Sarron of Team Gauloises Blondes Yamaha Mobil 1 finished 8th and 9th respectively. Norihiko Fujiwara finished 11th in the ninth round in Belgium and gained five championship points.

John Kocinski from Team Marlboro Yamaha Roberts took his first championship title this season riding the YZR250. Yamaha took their 13th manufacturer's title in the 250cc class while winning both the rider and the manufacturer titles in the 500cc and 250cc classes.

Kocinski finished the opening round in Japan in 14th despite starting on pole, which gave him only two series points. However, he won the following rounds in the USA, Spain and Italy to put himself on top in the ranking. From there on, he led the championship. Going into the final stages of the series, Kocinski took falls in the two races in France and Britain and no-pointed. This allowed Carlos Cardús (Honda) to take the lead in the championship. The battle for the title continued until the final round, with Cardús leading by five points. Kocinski started from pole position and took the lead near the end to win the race. Cardús was running 5th towards the end, but machine trouble forced him out of the race. Kocinski made an amazing turnaround to win the championship.