The concomitance of domestic violence and mental disorders is a controversial issue, from both a conceptual and clinical perspective. Many studies have documented the prevalence of mental illnesses in the population of male batterers, but few of them have taken into consideration the viewpoints of professionals working with batterers. This article presents the results of a qualitative study which aimed to explore the viewpoints of 11 professionals specialized in the treatment of male batterers, about the co-occurrence of domestic violence and mental disorders in their clients. Participants were questioned about their professional experiences with mentally disordered male batterers (MDMB) in a semi-structured interview. The participants believe that MDMB differ from other batterers because of their instability, and consider mental disorders as a significant risk factor in domestic violence. Participants’ viewpoints were observed through their verbal declarations and through their response to MDMB (avoidance, distanciation or integration). The participants’ declarations reflect the presence of paradoxes in the categorization and intervention with MDMB.