We investigated the presence of mutations/polymorphisms in the FSH receptor (FSHR) gene and their association with phenotype in women with premature ovarian failure (POF) in southern Brazil. Clinical and hormonal variables were determined in 36 46,XX women with primary or secondary amenorrhea before the age of 40 yr, FSH >40 IU/l and ovarian failure. DNA was isolated from peripheral leukocytes. Exons 6, 7, 9, and 10 of the FSHR gene were analyzed by PCR, restriction enzyme analysis, denaturing gradient gel electrophoresis, and direct sequencing. No inactivating mutations were found. Exon 10 had two polymorphisms, Ala307Thr and Ser680Asn (allelic frequency: 52.9 and 35.7%, respectively), which were not related to FSH, LH or estradiol serum levels. Ovarian size and small ovarian follicles on transvaginal sonography were not associated with FSHR genetic variants. In contrast, the last menstruation occurred significantly earlier in patients with the Ala307Thr polymorphism (A: age=33.3+/-7.1 yr vs T: 28.6+/-11.4 yr, p=0.04). In conclusion, we did not identify inactivating mutations in exons 6, 7, 9, and 10 of the FSHR gene. A high frequency of two polymorphisms that are in linkage disequilibrium was found in exon 10 of the FSHR gene. The presence of the Ala307Thr polymorphism may be associated with a more precocious onset of clinical disease.