The Government and authorities in Brazil were faced with a tragic accident in Goiania resulting from the misuse of a strongly radioactive medical teletherapy source not under radiation protection surveillance. The present report is divided into four parts: a chronology of destruction of the source, discovery of the accident and initial response; a description of the human consequences and the dosimetry and treatment of seriously exposed and contaminated persons; an account of the assessment of the environmental contamination and the remedial actions taken; and observations and recommendations. Appendices and annexes give an assessment of the effectiveness of international co-operation in the emergency response, and provide further information on: public communications; radiological survey equipment; guidelines for the discharge of patients; radiological protection; chemical decontamination; and the lessons learned.