In the early morning of 2 December 2013, a vehicle transporting a radiotherapy machine head containing a category 1, cobalt-60 radioactive source was stolen, resulting in radiation exposure to members of the public. This publication provides information about the circumstances of the incident and the response actions taken by the Mexican authorities, including dose assessments performed to identify the individuals exposed. The publication also describes the actions taken by the IAEA. Observations and lessons identified are presented.