A growing body of evidence documents a clinical pattern of harmful effects of therapist-patient sexual involvement. In addition, surveys suggest that 1 to 12% of all therapists may have engaged in this behavior at least once in their careers. In order to develop a more comprehensive research agenda, several of these studies are reviewed in terms of inferences that may or may not be drawn. Case studies and surveys may provide for inference of clinical harm and syndrome, but they are limited in terms of generalizations about incidence in the overall population. A population approach coupled with case sampling may provide a useful tool by which to approximate a minimum level of incidence and of effects.