VEGF-dependant angiogenesis is crucial for follicular growth, and corpus luteum formation and function, in the primate ovary. In the ovary VEGF can be hormonally regulated but in other systems the main regulator of VEGF expression is hypoxia. We hypothesized that hypoxia was involved in the regulation of angiogenesis in the cycling ovary. We therefore used immunohistochemistry to localize HIF-1 in the marmoset ovary across the ovarian cycle. We also investigated the effect of VEGF inhibition, using VEGF Trap (aflibercept), on HIF-1 localization during the follicular and luteal phases of the cycle. Finally we studied the effect of chorionic gonadotropin stimulation of the corpus luteum during early pregnancy. Nuclear HIF-1 staining was largely absent from normally growing pre-antral and antral follicles. However, there was marked up-regulation of nuclear HIF-1 in the granulosa cells at ovulation that persisted into the early corpus luteum. Mature corpora lutea and those collected during early pregnancy had minimal nuclear HIF-1 staining. The inhibition of VEGF in the mid-luteal stage resulted in a time-dependent up-regulation of luteal nuclear HIF-1 staining (p<0.05). There was never any nuclear HIF-1 in the theca cells of the follicle but VEGF Trap treatment during the follicular (p<0.001) or luteal (p<0.001) phase increased the proportion of antral follicles with nuclear HIF-1 staining in the granulosa cells. These results indicate that HIF-1 is up-regulated after vascular inhibition, using VEGF Trap, in the follicle and corpus luteum. However it is also acutely up-regulated during ovulation. This suggests a role for HIF-1 in both hypoxic and hormonal regulation of ovarian VEGF expression in vivo.