&NA;Four women with phenotypic features of Turner's syndrome and with polycystic ovaries (PCO) are described. In addition to the phenotypic features, Case 1 had primary amenorrhea and small PCO, Case 2 had a 46,XX/45,X karyotype (Iymphocytes), Case 3 had enlarged PCO which contained a decreased number of oocytes, and Case 4 had enlarged PCO and was short in stature. These cases support the concept of a relation between PCO and the X chromosome. Some PCO may represent an intermediate condition in a spectrum that extends from the streak gonad of Turner's syndrome to the normal ovary. Evidence for X chromosome involvement in PCO is summarized. The concept is advanced that at least some cases of PCO may be due to X chromosomal factors causing an abnormal follicular apparatus.