Negative effects of psychological treatments is a fairly unexplored area of clinical research. Previous investigations have indicated that a portion of all patients experience negative effects in terms of deterioration and various adverse events. Meanwhile, evidence suggests that many clinicians are untrained in identifying negative effects and unaware of the current research findings. The objective of the current study is thus to investigate clinicians' own perspectives and experiences of possible negative effects of psychological treatments. An invitation to participate in an anonymous online survey consisting of 14 open-ended questions was distributed via three mailing lists used by clinicians that primarily identify themselves as cognitive behavior therapists. The responses were analyzed using a qualitative method based on thematic analysis. In total, 74 participants completed the survey. A majority agreed that negative effects of psychological treatments exist and pose a problem, and many reported having experienced both deterioration and adverse events among patients in their own practice. The thematic analysis resulted in three core themes: characteristics of negative effects, causal factors, as well as methods and criteria for evaluating negative effects. The clinicians recognize that negative effects exist, but many are unaware of the current research findings and are unfamiliar with methods and criteria for identifying and preventing deterioration and adverse events. The results provide evidence for further dissemination of the present knowledge regarding negative effects, particularly during basic clinical training, as well as the need for raising awareness of the available methods for identifying and preventing negative effects.