A divisive law from the outset, the diminished responsibility defence has continued to arouse criticism since its inception over fifty years ago under section 2 of the Homicide Act 1957. Increasing pressure from academics, practitioners, and mental health professionals, among others, to restructure the law has resulted in a reformulation of the wording of section 2 under the unassuming auspices of section 52 of the Coroners and Justice Act 2009. This paper examines the new definition of diminished responsibility on two levels: the broader context and structural significance of the Act and section 52’s place within it; and, the technical detail of the section itself. In so doing, consideration is given as to whether the new law appeases the critics of the old, in addition to whether the Government has succeeded in bringing to bear its objectives of clarity, fairness and effectiveness.