['Many cycling women with elevated basal FSH level have been discouraged from undergoing IVF treatment. This is because elevated basal FSH is associated with poorer assisted reproduction treatment outcome. It has been argued that high FSH reflects not only reduced ovarian reserve but also poor oocyte quality. The aim of this study is to assess the value of treating cycling women who have elevated basal FSH and to assess the reasons for the reduction in both pregnancy rate (PR) and live birth rate (LBR).', 'Between January 1997 and December 2001, 2057 patients underwent 3401 consecutive IVF/ICSI cycles in which the basal level of FSH (days 2-4) was determined at an earlier cycle. Analysis, however, was only performed for a single cycle per patient. All cases were divided into four cohorts according to FSH levels: group A, FSH <10 IU/ml; group B, 10.1-15 IU/ml; group C, 15.1-20 IU/ml; and group D, FSH >20 IU/ml. Each group was stratified further into subgroups according to age, < or =38 and >38 years.', 'Both PR (A, 32.3%; B, 19.8%; C, 17.5%; and D, 3%) and LBR (A, 24.7%; B, 13.2%; C, 13.8%; and D, 3%) were significantly reduced in the higher FSH level groups. LBR was significantly higher in the younger subgroups (A, 32.2%; B, 21.8%; C, 20%; and D, 16.7%) as compared with the older subgroups (A, 12.1%; B, 8.3%; C, 10.5%; and D, 0%). Higher levels of FSH were significantly associated with more cycle cancellation, a larger amount of gonadotrophin required to achieve follicular maturity, and a lower number of eggs collected, embryos available and embryos transferred. In all cases, however, there was no significant correlation between FSH levels and fertilization rate or miscarriage rate. Younger cycling women with elevated FSH had significantly higher LBR compared with older women with normal FSH (21.2% versus 12.1%). Furthermore, the cumulative LBR after three cycles in these younger patients with elevated FSH levels was 49.3%.'] Does an elevated basal FSH reflect a quantitative rather than qualitative decline of the ovarian reserve?