An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries.

In humans, women have approximately 200,000 to 300,000 follicles at the time of puberty,[1][2] each with the potential to release an egg cell (ovum) at ovulation for fertilization.

These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single competent oocyte in humans.

[7] The granulosa cells, in turn, are enclosed in a thin layer of extracellular matrix – the follicular basement membrane or basal lamina (fibro-vascular coat in picture).

In humans, oocytes are established in the ovary before birth and may lie dormant awaiting initiation for up to 50 years.

In a larger perspective, the whole folliculogenesis from primordial to preovulatory follicle is located in the stage of meiosis I of ootidogenesis in oogenesis.

Presently, ovarian follicle volumes can be measured rapidly and automatically from three-dimensionally reconstructed ultrasound images.

[11] Rupture of the follicle can result in abdominal pain (mittelschmerz) and is to be considered in the differential diagnosis in people of childbearing age.

[15] Animal studies have generally shown correct imprinted DNA methylation establishment in oocytes resulting from follicle culture.