This study describes the use of reliable scales to rate the clinical skills of mental health nurses when working with individuals and families with severe mental health problems. The Cognitive Therapy Scale and the Schizophrenia Family Work Scale were adapted for the study and were shown to have good inter-rater reliability when assessing audio-taped interviews carried out by mental health nurses during their usual course of work with patients with severe mental health problems and their families. The sample of mental health nurses studied were shown to have significantly better general therapy skills than specific cognitive therapy technical skills. The implications for training are discussed.