A brief introductory part is followed by a discussion of the age of the bitch and that stage of the oestrous cycle, during which ovariohysterectomy can best be performed. The various indications for ovariectomy and ovariohysterectomy are reviewed. A number of important anatomical features are briefly referred to and the technique of ovariohysterectomy is described in detail. Attention is paid to a number of complications such as haemorrhage during or after operation and the escape of infected contents of the uterus into the abdominal cavity. Finally, the possible effects of ovariohysterectomy, such as a gain in weight, a change of character, incontinence of urine and the appearance of an infantile vulva associated with pruritus vulvae, are discussed.