The relationship between dogs and humans is ancient and mutually beneficial. Dogs have served people well as companions, workmates, guides, and protectors. However, on occasion, dogs may injure humans through biting or may transmit pathogens resulting in a large number of problems ranging from a trivial rash to life-threatening bacteremia. Given that there are more than 80 million pet dogs in the United States, it is worth knowing the potential problems that can result from canine exposure. Annually, almost 5 million people in the United States suffer a dog bite. Dog bite wounds become infected up to 15% of the time. In those who have had a splenectomy, a dog bite may transmit the bacterium Capnocytophaga canimorsus, leading to life-threatening bacteremia. Other illnesses that humans can acquire from dog contact include ringworm, diarrheal disease (salmonellosis, campylobacteriosis, and intestinal parasites), leptospirosis, brucellosis, Q fever, visceral larva migrans, and echinococcosis. Evidence exists that the family dog may serve as a reservoir for uropathogenic Escherichia coli that can lead to urinary tract infections among human household contacts. In this article we discuss dog-related infectious diseases as well as measures to minimize dog-associated illness (e.g., do not disturb sleeping dogs; HIV-infected persons who wish to acquire a puppy should have the dog's stool checked for Cryptosporidium).