The Malinois is generally speaking a healthy dog. As mentioned in relation to finding a good breeder, hip dysplasia and hereditary cataracts are problems that all breeding Malinois should be screened for in order to produce healthy puppies, and yes both conditions do occur in Malinois. However, both are rare -in particular when the dogs come from a health testing breeder. It should also be noted however that over exercising a growing puppy can actually cause both hip dysplasia and elbow dysplasia, so care should be taken to adjust the amount of exercise to the age of the dog. (See the page about exercise.)
Epilepsy do occur in all the Belgian Shepherd varieties. Unfortunately there is no test to detect epilepsy and so the only way to prevent it is to breed from dogs where you know that the parents, grandparents, littermates etc were healthy. Thankfully, epilepsy isn't common either, and research is being carried out to hopefully develop a DNA test one day.
Cancerous tumours is something seen in Malinois from time to time, in particular mammary tumours in older bitches. Other tumours can also occur, as in any breed of dog.
On average, the Malinois lives between 12-15 years.