It's so rewarding watching your happy, healthy puppy bounding around, having fun and enjoying life. However, at some stage nearly all puppies are going to experience a bout of vomiting or diarrhea. Often there is nothing to worry about. Puppies and grown up dogs have sensitive stomachs and can vomit in reaction to something very minor. Alternatively it could be an indication of something more serious. There are many reasons why a puppy may vomit or suffer from diarrhea and some of the following causes can help you decide whether or not you should seek medical help.