Preheat the oven to 375˚. Divide the brussels sprouts between 2 baking sheets and toss with the olive oil. Sprinkle with the salt and pepper and roast until browned, 25 to 30 minutes.
Meanwhile, combine the balsamic vinegar and sugar in a small saucepan. Bring to a boil, then reduce the heat to medium-low and cook, stirring frequently, until very thick, 15 to 20 minutes. (You should have about 1 cup.)
Drizzle the balsamic reduction over the roasted brussels sprouts, then sprinkle with the dried cranberries. Toss and transfer to a bowl.
