Eddie Lawson would recapture the championship from Wayne Gardner in a season that witnessed several fierce duels. Two newcomers joined the Grand Prix circuit with Americans Wayne Rainey and Kevin Schwantz each winning races in their first full year. This was Rainey’s debut in the 500s; he had ridden a 250 in 1984 and gotten 1 podium of 12 starts. Alan Cathcart’s pre-season assessment in Cycle News was that “Rainey is a good rider, but he’ll never be a great rider. And he’ll certainly never be a Randy Mamola.”
The V4 machines used by the factories were extremely powerful and in combination with rigid chassis produced power slides that sometimes caused violent highsides, throwing the riders into the air. Cagiva joined the racing with Randy Mamola as their rider. The first United States Grand Prix in 23 years was held in Monterrey, California.
Sito Pons beat out fellow countryman Juan Garriga for the 250 title winning four races to Garriga's three. Spain's Jorge Martinez captured double championships in the 80 and 125 classes for the Spanish firm Derbi.