The different types of ambisexual development have been described. It is most important in earliest infancy to differentiate, on the basis of the 17-ketosteroid excretion, female pseudohermaphroditism due to congenital adrenal hyperplasia from other forms of ambisexual development. The female pseudohermaphrodites should be reared as girls and treated with cortisone according to the methods described. Surgical exploration is not indicated. If the clitoris is enlarged it should be removed before school age and the urogenital sinus corrected to form a separate vagina. With cortisone therapy continued normal female development can be assured. When the adreno-genital syndrome has been excluded, all patients with ambiguous genitalia should be submitted to careful urethroscopic study and exploratory laparotomy. This applies also to individuals who appear to be cryptorchid males with hypospadias and those resembling females with gonads in the groins or labia. These procedures should be carried out in the earliest months of life and a definite decision made as to the sex in which the child is to be reared. Abundant evidence has been accumulated that an individual's gender role and erotic orientation are established through the cumulative experiences of years of living as a boy or a girl. Irrespective of chromosomes, gonads or hormones, the child who from earliest infancy has been steadfastly accepted as a girl or as a boy, particularly if the external genitals have been altered to conform to this sex, will not question his own gender and will conform to the habits and behavior of the sex of rearing. When there is prolonged doubt and uncertainty on the part of the parents or when a change of sex is imposed after an early age and before late adolescence the child will be confused and perplexed and psychologic difficulties result. Accordingly, every effort should be made in early infancy to decide the sex of rearing and the parents should be given support, guidance and reassurance. Necessary corrective operations should be undertaken as early in life as possible. No change from the original decision should be made in later childhood. It is advisable to select the sex of rearing according to the anatomic structure of the external genitalia rather than the type of gonads or the sex chromosomal pattern. To attempt to make a boy of an individual who does not have a fairly well-developed phallus is unwise and condemns the patient to a life of misery. Male pseudohermaphrodites who have external genitalia of female configuration invariably feminize at puberty, so that orchidectomy is not necessary to prevent masculinization. Its only indication might be to avoid the possible risk of testicular malignancy. Male pseudohermaphrodites whose genitalia resemble the male or are ambiguous may either masculinize or feminize at puberty. If it is decided to raise such a child as a female because of the small size of the phallus, orchidectomy may be performed in infancy to avoid the risk of masculinization or it may be postponed until masculinization begins. The former course often seems preferable. At puberty estrogen should be given in doses adequate to develop female sex characteristics. In these cases gonadectomy cannot be considered a mutilating operation or one which deprives the patient of fertility. On the contrary it is one which enables the patient to continue as a reasonably normal individual in the sex in which he has been reared and prevents the disastrous psychologic upheaval of a sex reversal.