All pedigree dogs have some form of illness, you can't avoid it (this is why mongrels often live longer than pedigree dogs). The common ailments that GSDs have result from the interbreeding required early in the breed's creation.
A common issue is hip and elbow dysplasia which may cause the dog pain in later life, along with arthritis. If you are thinking of getting a GSD please get a hip and elbow score done. The lower the score, the better.
Scoring for the elbow is 0/1/2/3 with the highest number being the worst.
In a GSD try and keep the hip score under 10. Their scores will get higher as they get older and anything over a 20 is horrible.
Another common ailment for GSDs are ear infections because their ears are so large and open.
Worryingly, GSDs and all large breed dogs are prone to bloat. Bloat is where the stomach becomes overstretched by excessive gas content. This may be caused by a twist in the stomach which doesn't allow gas to escape. Deep chest breeds are especially at risk.
Mortality rates range between 10-60% even with treatment. With surgery, the mortality rate ranges between 15-33%
GSDs also suffer from Spinal Disorders, Low Thyroid problems, Skin Allergies (allergies to fleas etc), Canine Epilepsy, Exocrine Pancreatic Insufficiency and Pansotitis, which is seen in large boned dogs.
A GSD is lean and full of muscle. You should be able to feel its rib bones but not see them.
The average lifespan for a GSD is between 7-10 years and 10-13 years.