This article reviews literature on negative outcome in psychotherapy for adult, non-psychotic individuals. Patient, therapist, and therapy variables are examined, and tentative conclusions are drawn from the existing data. Patients who are borderline or obsessive-compulsive, have severe interpersonal difficulties, are poorly motivated, or who expect psychotherapy to be painless have been found to be at risk for deterioration. On the part of the therapist, lack of empathy, underestimation of the severity of the patient's problems, negative counter transference, poor technique, high concentrations of transference interpretations, and disagreement with the patient about the therapy process all have been associated with negative outcome. Cestalt therapies have produced higher rates of deterioration than other psychotherapy modalities. Issues in research methodology are discussed, including identification of negative responders, outcome measurement, identification of variables related to negative outcome, and the role that ethical dilemmas play in research.