Lyme disease usually begins with a characteristic skin lesion, erythema chronicum migrans, accompanied by 'influenza-like' or 'meningitis-like' symptoms. Some patients later develop cardiac abnormalities such as atrioventricular heart block or myopericarditis, neurologic complications, or intermittent attacks of arthritis. The causative agent, the Lyme disease spirochete Borrelia burgdorferi, is transmitted by Ixodes dammini or related ixodid ticks. Antibiotic treatment with tetracycline or penicillin is usually curative. We report the case of a woman who developed Lyme disease during the first trimester of pregnancy. She did not receive antibiotic therapy. Her infant, born at 35 weeks gestational age, died of congenital heart disease during the first week of life. Histologic examination of autopsy material showed the Lyme disease spirochete in the spleen, kidneys, and bone marrow.