The year was the swansong for the gigantic 1971-78 Cadillac Eldorado and the dawn of the dubious diesel option, but it was also the second best sales year ever for Cadillac. There were seven models in the lineup, including several simulated convertibles with canvas tops sewn on. The successful smaller Seville was fitted with an Oldmobile V-8, while the larger cars featured the 180 bhp 425 cid V-8. The Eldorado coupe notched 46,816 sales for the year.

There were four different levels of Eldorado for 1978. The base coupe could be upgraded with a Special Cabriolet edition, or buyers could choose the Eldorado Custom Biarritz. The new Eldorado Custom Biarritz Classic was an over-the-top version of that, with bright two-tone paint and special interior appointments. It was powered by the V-8 introduced in 1977. Base price was now $11,921.

The 1978 Eldorado was available with optional leather interiors and came with a bench front seat with folding center armrest, or optional 50/50 Dual Comfort front seat with dual armrests. Automatic climate control was standard, along with a more efficient compressor (which switched off when not needed) power door locks, a 6-way power adjustable seat, an AM/FM stereo radio, and steel-belted radial tires.

Popular options included electronic fuel injection, airbag, padded vinyl roof, power sunroof, AstroRoof, tilt/telescopic steering column, cruise control, intermittent wipers, remote trunk release, rear window defogger, self-seeking AM/FM stereo with rear control ($340), AM/FM stereo with tape player, AM/FM stereo with CB ($281), tinted glass, heated front seats, and automatic headlight dimer.

Cadillac finished up in 10th place for 1978 sales, barely behind Chrysler and ahead of Lincoln and AMC. The division might have done better, but the Linden, New Jersey plant was shut down for three months to prepare for the new downsized E-Body Eldorado, Toronado, and Riviera models.