Ford earned its biggest profit in more than a decade in 2010 as robust vehicle sales and years of cost cuts paid off. But disappointing fourth-quarter results rattled investors Friday and sent the company’s stock price lower.

Ford shares fell 12 percent to $16.63 in late morning trade after the company missed analysts’ expectations. The reaction showed the difficulties Ford faces, even though it’s remade itself over the last four years.

Ford’s net income totaled $6.6 billion, or $1.66 per share last year, more than double the $2.7 billion, or 86 cents, from 2009. Before charges for debt reduction and the discontinuation of its Mercury brand, Ford would have earned $1.91 per share, short of the $2.05 analysts expected.

Ford’s fourth-quarter profit also missed Wall Street’s forecasts. Net income dropped 79 percent to $190 million, or 5 cents per share. Results included a big charge for lowering its debt. Without it, Ford would have earned 30 cents per share, still far below the 48 cents analysts anticipated.

Ford said it warned investors about the one-time charges but didn’t keep them updated when it decided to pull back on incentive spending in Europe, which led to a drop in sales and profits there. The company said it also spent more marketing new products like the Ford Explorer in the fourth quarter than some analysts had anticipated.