Position a rack in the center of the oven and heat the oven to 425 degrees F.

Cut the sausages in half on a sharp angle and arrange them on a large rimmed baking sheet or in a shallow roasting pan. Add the grapes to the pan. Sprinkle the vinegar over the sausages and grapes, season with salt and a generous amount of black pepper, and toss so that everything is evenly seasoned.

Roast, turning with a spatula after 15 minutes, until the sausages are browned and cooked through (cut into one to check), 35 to 40 minutes total. Scatter the parsley over the top, stir to mingle all the juices, being careful not to crush the grapes, and serve.