1. Laboratório de Pesquisas Clínicas do Centro de Pesquisas René Rachou. 2. Instituto de Tecnologia em Imunobiológicos/Biomanguinhos da Fundação Oswaldo Cruz. 3. Secretaria de Saúde de Minas Gerais. 4. Secretaria Municipal de Saúde de Contagem, MG. Endereço para correspondência: Dra. Ana Rabello. Laboratório de Pesquisas Clínicas/Centro de Pesquisas René Rachou/FIOCRUZ. Av. Augusto de Lima 1715, 30190-002 Belo Horizonte, MG E-mail: firstname.lastname@example.org Recebido para publicação em 15/5/2001. Abstract In August/1999, a group of 14 adults from the staff of a private hospital in Contagem – Minas Gerais State, Brazil, received unintentionally a 25 times concentrated dose of the 17-DD yellow fever vaccine (BioManguinhos), due to a mistake at the reconstitution step. All patients were clinically and laboratorially evaluated at days 5, 13 and 35 post vaccination. Frequency of side effects and clinical observations of this group of individuals were not different from the observed in recipients immunized with normal doses of the vaccine. At the second and third evaluation none of the subjects reported symptoms. None of the patients presented abnormalities at the physical examination at none of the time points and in all cases the blood examination was normal, except for a reduced number of platelets that was detected in one subject at the first and second evaluation and reverted to normal at third evaluation. At the first evaluation point, 8 subjects were serum negative and 6 serum positive for yellow fever at the plaque reduction neutralization test. In 5 subjects the observed titre was 10 times higher as the baseline of 2.36 Log10 mUI/ml. The samples collected at second and third evaluation (13th and 35th days) demonstrated that all subjects responded to the vaccination with the exception of one that did not present a positive result in any of the samples collected. This evaluation confirms the safety of the 17DD yellow fever vaccine. Key-words: Yellow fever. Vaccination. Safety.