Cook beef tenderloin for 40 minutes to 70 minutes depending on the cut's size and desired doneness. With the oven at 425 degrees Fahrenheit, cook a 1- to 3-pound tenderloin to medium rare for about 40 minutes or to medium for about 50 minutes.
When cooking a 4- or 5-pound tenderloin, roast for about 60 minutes for a medium rare roast or about 70 for a medium done roast. To make the tenderloin extra juicy and flavorful, brown the meat with olive oil in a large skillet over medium-high heat, then transfer to a rack in a shallow roasting pan. Roast the meat to the desired doneness, and let it stand for 15 minutes before slicing and serving.