Countertransference reactions are defined as including the therapist's total response to the client, conscious and unconscious. If not recognized, these reactions can create problems for the therapist and affect the therapeutic process. A case history is presented that involved a female therapist's work with a male offender. The case history explores some of the reactions and difficulties professionals may encounter in work with sex offenders: recognition of one's own sadistic thoughts; need to manage key polarities in transference and countertransference; and need to develop an empathic relationship yet not collude with the offender's denial. The case history shows that therapist fantasies, reactions, and interventions can provide information, perspective, and understanding that are valuable to the client, to the professional involved, and to the intervention and treatment process. Polarities in the therapist- client relationship are noted, and the importance of developing an empathic relationship in sex offender treatment is stressed.