104 patients with erythema migrans disease (EMD), 7 patients with borrelia lymphocytoma (BL), and 21 patients with acrodermatitis chronica atrophicans (ACA) were prospectively followed for a median of 20, 14, and 12 months, respectively. 99 patients with EMD and 6 with BL were treated with antibiotics early for their illness. 72 patients with EMD had 1 to 10 constitutional symptoms besides the erythema migrans, 32 had erythema migrans alone, and a child with BL had urticaria. Out of 39 patients with EMD, 23 acquired arthralgia, 18 signs and symptoms consistent with neurologic manifestations and 8 with cardiac involvement before or after therapy. 4 patients with EMD and 1 with BL had up to 10 multiple erythema migrans lesions. 3 patients with EMD experienced a reinfection and 1 with ACA a relapse. Several patients with ACA developed signs and symptoms consistent with neurologic, cardiac and joint involvement, and 2 had a history of EMD. Elevated antibody titers against Borrelia burgdorferi were present in 48% of 69 patients with EMD, 5 with BL and 11 with ACA, and in 93% of another group with EMD, 2 with BL and 10 with ACA, when tested against other borreliae. Increased values of the ESR, IgG, IgA and IgM were found in more patients with ACA than with EMD. The median of IgA and IgM was significantly higher in ACA than in EMD. Borreliae were found in brain and liver of a newborn. Early EMD appears to be quite similar to early Lyme disease.