Tick-borne diseases are the most common vector-borne illnesses in the United States. Lyme disease is the most common, but several others also occur. The ehrlichioses have only been identified as agents of human disease in the United States in the past few decades, and knowledge about them is still evolving. Rocky Mountain spotted fever is relatively common and can be severe, especially in children, if the diagnosis is not made quickly. Tularemia has long been known to cause disease in humans, but there is renewed interest because of its potential as a biologic warfare agent. These diseases can be severe or even fatal. Most of them are easily treatable when identified early. These diseases result from a variety of infectious agents including bacteria, rickettsia, viruses and protozoa, or they may be caused by substances produced by the tick. Most of these diseases present initially with nonspecific symptoms and are often difficult to recognize. Few definitive diagnostic tests are available. Therefore, knowledge of the epidemiology and common presentations, as well as the diagnostic options and treatments available, are important issues for family physicians.