In Zaire, we studied 180 patients with Mycobacterium ulcerans infections and found 14 with a history of antecedent trauma at the site of the lesion (e.g., gunshot and land mine injuries, penetrating wood splinters, and scorpion stings). Two patients developed lesions following hypodermic injections. We believe that trauma is an important mode of transmitting M. ulcerans infections, or of introducing the etiologic agent into the dermis of subcutaneous tissue from superficially contaminated skin.