The absence of uterus has been regarded by a number of authors as a condition for the diagnosis of testicular feminization, although cases with a rudimentary uterus have been reported. However, their number within the framework of this syndrome cannot be exactly determined. In the present report on a 22 year-old patient with testicular feminization and uterus bicornis solidus a double uterus malformation identical with that described in the Mayer-Rokitansky-küster syndrome was found. Forms of testicular feminization with rudimentary uterus in genetically-male individuals may be explained by the absence of androgens, or the absence of reactivity on the part of the target organ, and a simultaneous disturbance (lessening) of the function of the so-called X-factor (oviduct repressor) during early embryonal development. Our own observations, as well as reports in the literature, suggest a theory according to which testicular feminization may be regarded as a series of morphological variants, from male-oriented forms with vaginal aplasie, hypertrophy of the clitoris and male distribution of pubic hair, to female-orientated ones with a vagina of normal length and a rudimentary uterus. The absence of a uterus as a condition for the definition of the syndrome can be maintained only so far as no cases have, as yet been observed with a normally-developed uterus in a typical position. The karyogram showed a small Y-chromosome. Functional anomalies may only be surmised, since Y-anomalies are frequent (3% in a random collection). The morphology of the testes mirrored the functional embryonal insufficiency (pre-pubertal, undifferentiated testicular tissue with a varying amount of stroma and Leydig cells); the basal excretion of testosterone, 17-ketosteroid fractions and pregnane in the 24-hour urine was within the normal range for males. Oestrogen production over and above the "adrenal values" was also present. The values for plasma testosterone, which are in accordance with those of males of a similar age, are considered as indicating the importance of "androgen resistance in the periphery" as a factor in the aetiology of testicular feminization.