Preheat oven to 350 degrees F (175 degrees C). Grease 12 muffin cups or line with muffin liners.
In a large bowl, combine flour, baking soda and salt. In a separate bowl, combine bananas, sugar, egg, butter and vanilla. Stir the banana mixture into the flour mixture just until moistened. Fold in chocolate chips.
Fill muffin cups right to the top and bake for 20 to 25 minutes in the preheated oven. Muffins are done when toothpick inserted in center comes out clean.