OBJECTIVES: To quantify the number of doctors charged with manslaughter in the course of legitimate medical practice and to classify cases, as mistakes, slips (or lapses), and violations, using a recognized classification of human error system. DESIGN: We searched newspaper databases, Medline, Embase, and the Wellcome library catalogue to identify relevant cases from 1795 to December 2005. SETTING: Medical practice in the United Kingdom. MAIN OUTCOME MEASURE: Number of doctors charged with manslaughter in the course of medical practice. RESULTS: We identified 85 doctors charged with manslaughter since 1795. The number of doctors charged was relatively high in the mid-19th century and the inter-war years, and has dramatically increased since 1990. Sixty of the doctors were acquitted, 22 were convicted, and three pleaded guilty. Most doctors were charged as a consequence of mistakes (37) or slips (17), and a minority because of alleged violations (16). CONCLUSIONS: The number of doctors prosecuted for manslaughter has risen steeply since 1990, but the proportion of doctors convicted remains low. Prosecution for deliberately violating rules is understandable, but accounts for only a minority of these cases. Unconscious errors--mistakes and slips (or lapses)--are an inescapable consequence of human actions and prosecution of individuals is unlikely to improve patient safety. That requires improvement to the complex systems of health care.