The family physician is occasionally called into consultation when one of his patients, a hitherto respected citizen, becomes arrested for a sexual offence. In such circumstances the relatives, friends or legal advisers of the accused are often prompted to raise a defence of insanity, mental disorder or defect in answer to the charge. On examination the physician may find such evidence. If not he may regard the patient as being psycho-pathological, but unless he has devoted time to the consideration of the subject, and is also well acquainted with insanity, amentia and border-line states in his daily work, he may not feel sufficient confidence in his general knowledge and medical experience to face with equanimity the prospect of a severe cross-examination in the witness-box on an admittedly difficult and controversial subject. I know the family physician may, in such cases, feel embarrassed, and I propose to attempt to bring before you certain matters for consideration which it seems well to bear in mind when inquiring into the mental condition of persons accused of sexual crime, and which I suggest throw some light upon actions that otherwise appear unusually obscure.