Most fruits are high in sugar, some more so than others. Even though the sugar in fruit is "natural", it still spikes your blood sugar, which causes the pancreas to pump out more insulin. If this happens regularly, your body may become resistant to insulin, which could lead to type II diabetes.
It's best to limit fruit to 1-2 servings/day and try to stick with things like berries, apples, pears, which are chock full of fiber.