Lyme disease was first recognized in 1975 after researchers investigated why unusually large numbers of children were being diagnosed with juvenile rheumatoid arthritis in Lyme, Connecticut, and two neighboring towns. The researchers discovered that most of the affected children lived and played near wooded areas where ticks live. They also found that the children's first symptoms typically started in the summer months, the height of the tick season. Several of the patients interviewed reported having a skin rash just before developing their arthritis. Many also recalled being bitten by a tick at the rash site.

Further investigations discovered that tiny deer ticks infected with a spiral-shaped bacterium or spirochete (which was later named Borrelia burgdorferi) were responsible for the outbreak of arthritis in Lyme.

In Europe, a skin rash similar to that of Lyme disease had been described in medical literature dating back to the turn of the 20th century. Lyme disease may have spread from Europe to the United States in the early 1900s, but health experts only recently recognized it as a distinct illness.

Small rodents and deer play an important role in a deer tick's life cycle.

Both nymphs and adult ticks can transmit Lyme disease-causing bacteria. The recent increase of the deer population in the Northeast and of housing developments in rural areas where deer ticks are commonly found probably contributed to the disease's increased spread.

The number of reported cases of Lyme disease as well as the number of geographic areas in which it is found have increased. Lyme disease has been reported in nearly all states in the United States, although more than 95 percent of all reported cases are concentrated in the coastal Northeast, mid-Atlantic states, Wisconsin, Minnesota, and northern California. Lyme disease is also found in large areas of Asia and Europe.