The author offers a 40-year perspective on the observation and study of negative effects from psychotherapy or psychological treatments. This perspective is placed in the context of the enormous progress in refining methodologies for psychotherapy research over that period of time, resulting in the clear demonstration of positive effects from psychological treatments for many disorders and problems. The study of negative effects--whether due to techniques, client variables, therapist variables, or some combination of these--has not been accorded the same degree of attention. Indeed, methodologies suitable for ascertaining positive effects often obscure negative effects in the absence of specific strategies for explicating these outcomes. Greater emphasis on more individual idiographic approaches to studying the effects of psychological interventions would seem necessary if psychologists are to avoid harming their patients and if they are to better understand the causes of negative or iatrogenic effects from their treatment efforts. This would be best carried out in the context of a strong collaboration among frontline clinicians and clinical scientists.