Objective: To evaluate the clinical significance of LH in the form of a mutant β-subunit in women with polycystic ovary syndrome (PCOS). Design: Prospective, controlled study. Setting: University hospital. Patient(s): Thirty healthy women and 30 women with PCOS. Intervention(s): Clinical, ultrasonographic, and hormonal findings were used to define PCOS. Nucleotide mutations within codons 8 and 15 in the LH β-subunit gene (Trp8 → Arg and Ile15 → Thr) were analyzed with the use of polymerase chain reaction and subsequent restriction fragment length polymorphism. Main Outcome Measure(s): Serum levels of gonadotropins, androgens, E2, and prolactin were determined, and the results of restriction fragment length of polymorphism were analyzed. Result(s): Five women in the control group and one woman in the PCOS group were found to be affected by the LHβ gene mutations. No difference was observed in serum androgen and E2 levels between the affected women and 25 healthy women who were homozygous for the wild-type LH. However, women whose serum LH levels were ≤ 5.1 mIU/mL had a higher risk of having mutant LH. Conclusion(s): The frequency of LH mutations in women with PCOS is similar to that in healthy women. The presence of the variant does not cause any significant change in serum levels of androgens and E2.