If your tomatoes have brown or black spots on their leaves, you may have early blight.  This is a common disease that disfigures old leaves and tomatoes. Remove the leaves as soon as you see spots form, this may prevent it from spreading to the rest of the plant. Spreading mulch over the soil and keeping the leaves dry can also be effective preventive measures. Spraying with Bonide's Tomato and Vegetable 3-in-1 can help if caught early.