By their very nature, overseas medical missions (and even domestic medical charities such as "free clinics") are designed to serve "vulnerable populations." If these groups were capable of protecting their own interests, they would not need the help of medical volunteers: their medical needs would be met through existing government health programs or by utilizing their own resources. Medical volunteerism thus seems like an unfettered good: a charitable activity provided by well-meaning doctors and nurses who want to give of their time, skills, and resources to help those who would not otherwise be able to take care of their medical needs. In this article, I argue that if medical volunteerism is to be "good," however, it must always meet certain basic ethical requirements. These requirements may be (and perhaps often are) overlooked in the rush to organize and carry out short-term medical missions. I illustrate my point with special reference to short-term medical missions designed to provide surgical repair of obstetric vesico-vaginal fistula, a condition in which the tissues that normally separate the bladder from the vagina are destroyed by obstetric trauma, leading to continuous and unremitting incontinence in the affected woman.