Great Danes were originally bred hundreds of years ago by crossing mastiffs with greyhounds. Designed to assist in hunting wild boars, they were created with a good balance of size, strength and speed. Although great danes are no longer used for hunting, they still maintain these characteristics. The average dane measures around 32 inches at the shoulder. They typically weigh around 150 lbs.  
Their life span is usually between 5 and 13 years. Breeding plays a big part in determining this. Great Danes that have not been carefully bred to avoid genetic problems such as hip dysplasia, heart conditions, thyroid & liver problems, and bloat will probably not live as long as danes that have been bred from genetically healthy parents. Please select your breeder carefully and make sure the parents of your puppy are free of any health problems. Most of these conditions will not show up until a dog is 2-3 years old, so you're better off selecting a puppy who's parents are at least 2-3 years old and have been screened for these problems.
These guys are big eaters. Budget for about 40 lbs. of food a month, and keep in mind that EVERYTHING costs more when you have a dog this size...medications, jumbo sized toys and bones, heavy duty leashes, beds, etc. If your budget affords proper care of a great dane, they make excellent pets. These giant dogs have a very loving personality. I have never met a mean great dane. Although they will bark at strangers to protect you or their home, they are very sweet once they know there is no threat. Great Danes are mellow dogs, not hyper or overactive which makes them the perfect house dog. They love hanging out sleeping on the couch, but they are always up for a walk or a trip out to the store. Great Danes are extremely easy to train. They are very intelligent creatures, aiming to please every chance they get. Potty training and obedience training can be done in a few weeks with lots positive reinforcement.  
If you have small children and are considering a great dane, I recommend adopting an adult dog from your local great dane rescue society or humane society. Great Danes grow very quickly, and a 100 lb. six month old puppy bounding around the house can be too much for a crawling infant or toddler to keep up with. An adult will already be calmer, and their gentle nature makes them perfect family pets. Select your dog or puppy carefully - remember you are making a long-term commitment to properly care for him, and he will love you for life. Good luck!

Click Here to read the AKC Standard for Great Danes

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What to Look for in a Great Dane Breeder and Puppy