BACKGROUND: To determine the prevalence, age distribution, seasonality and clinical characteristics of Lyme-simile disease in Brazilians less than 15 years of age. METHODS. From July, 1998 to November, 2000, a cross-sectional study was conducted in 333 patients with skin rash and fever. Paired blood samples were collected for identification of the pathogens. Only 193 samples which were negative for other pathogens (Parvovirus B19 Human, Herpesvirus 6 Human, Measles, Rubella, Dengue, Scarlet fever and Enterovirus), were tested for borreliosis by Enzyme-Linked Immunosorbent Assay and Western-blotting. Other clinical, socioeconomic, demographic and climatic variables were studied. RESULTS: Prevalence of the disease was 6.2%(12/193). Of the variables studied, there was predominance in: <6 years old (83.2%); females (66.7%); being from the city of Franco da Rocha (58.3 %); and a summer/fall seasonality. The duration of care was 4 days. Signs and symptoms with statistical significance were itching; absence of lip notch and ocular pain; irritability and good clinical condition. Other clinical data presented were: pruritus (90%), irritability (80%) and fever (38 masculineC) (58.3%) with a duration of 1 to 3 days. Erythema was maculo-papular (40%), urticaria-like (25%) and scarlatiniform (16.7%), occurring predominately on the trunk (60%). There were no primary clinical evidences of Lyme-simile disease in the patients under study. The sensitivity and specificity of the clinical diagnosis as opposed to the laboratory diagnosis was zero. There was no initial clinical suspicion of the disease in the 10 cases studied and followed up for two years that showed no evidence of cardiologic or neurological complications. This is the first study of Lyme-simile in Brazilian children. CONCLUSION: Prevalence of Lyme-simile disease was low, and it was not remembered at the initial diagnosis of those with skin rash. However, practical knowledge is necessary, demanding increased medical attention.