In this paper the author gives a summary of the contributions made by Dr Estela Welldon to the Group Psychotherapy at The Portman Clinic. He describes how clinicians working at the Portman Clinic have evolved and adapted the principles and practices from group psychotherapy in order to work with perverse, violent, delinquent, transsexual and other specialist patient groups in what is described as ‘forensic group psychotherapy’. Attention is drawn to the selection of patients, composition of the group, particular differences of dynamic administration of the group, the style of the conductor, and the observed and expected group processes. The author describes his personal experience as a specialist registrar in forensic psychotherapy at the Portman Clinic working with Dr Welldon, and his continued work there as a consultant, and the continual development and evolution of forensic group psychotherapy.