In the 143 murder cases between January 1, 1997, and December 31, 2001, in which diminished responsibility was an issue and psychiatric reports were available, psychiatrists rendered 338 opinions on at least one aspect of diminished responsibility. A verdict of diminished responsibility was given in 118 of the cases. In 110 of these cases (93 percent), the verdict was rendered without a trial and therefore was not the result of a jury's decision. Only 8 of the 30 cases (27 percent) that went to trial resulted in a verdict of diminished responsibility. Half of the psychiatric reports (169) included a definite opinion on diminished responsibility; one-third (121) invited the court to draw a conclusion, and only 11 percent (36) provided relevant evidence without rendering an expert opinion on diminished responsibility. When there was an opinion or an invitation to make a finding on diminished responsibility, a trial was less likely. A trial was also less likely if there was consensus among psychiatrists brought into the case about what the verdict should be. Study data were obtained from psychiatric reports and files provided by the then Department of Constitutional Affairs (now the Ministry of Justice) on cases heard in the Crown Courts for the designated period. The study included only murder cases in which diminished responsibility was an issue and for which psychiatric reports were available. Researchers developed a reliable system for rating the presence/absence and strength of expression of a legal opinion in the psychiatric reports. Data were tested for a link between the nature and strength of psychiatric opinion and progression of the case to trial and verdict. 4 tables and 13 references