Vegetarian does not mean healthy. There are plenty of overweight, malnourished, unhealthy vegetarians around. Whether you are vegetarian, considering it, or perhaps confused on the issue, be aware that as a vegetarian you will need to spend more time, energy, and effort planning your meals and concerned about nutrition. This is especially true in most of the first world. In the third and to a lesser extend the second world, it's pretty easy to avoid meat as it's expensive and not a stable and still eat a balanced diet.
We probably all know a few vegetarians who are not the picture of health. Many vegetarians are overweight for example, and it's common to gain weight from becoming a vegetarian. I recently put on 15 pounds in 2 months of no meat.
Why does this happen? Typically from too many simple carbs from foods like pizza, pasta, potato chips, and more. These are far from healthy foods, especially when they start forming the basis of your diet. Running late? Do not consider grabbing a big bag of chips as breakfast or lunch!
It's also hard to get enough protein. Beans and rice are an excellent source, as is tofu. If you are eating seafood such as fish and clams or dairy like eggs and milk, they are also great protein sources.
You can't just assume vegetarian means healthy. Should you make this choice you will need to work at it and learn at least a little bit about nutrition? Don't go on the veggie pasta, pizza, and potato chip diet like I did and expect to be healthy or thin!