US consumers continued the trend away from small cars and sedans, but appeared increasingly squeezed by higher interest rates and price tags.
With low unemployment levels and a strong economy, America's big three auto makers reported a mixed picture.
GM and Ford notched declines. Fiat Chrysler's US subsidiary soared.
GM, the biggest of the US auto makers, reported a 2.7 percent sales dip in the fourth quarter and a 1.6 percent decline for 2018 -- despite selling more crossover SUVs than in 2017.
Ford also struggled. Sales were down 8.8 percent in December to end the year 3.5 percent lower than 2017. It, too, sold more of its larger vehicles, including F-Series pickups and SUVs.
FCA US, Fiat Chrysler's US subsidiary, improved its annual total by nine percent -- fruits of its new focus on larger vehicles. The company's sales rose 14 percent in the final month of the year.
"This year's performance underscores the efforts we undertook to realign our production to give US consumers more Jeep vehicles and Ram pickup trucks," FCA US's sales chief Reid Bigland said in a statement.
Another industry giant, Toyota, also recorded US sales slumps in December and the year -- 0.9 percent and 0.3 percent, respectively.