Follicular lymphoma is regarded as reticulosarcoma in situ. Tumor nodules are represented by neoplastic foci of the tumor tissue. They can show the structure of lymphoblastic, reticulocellular and polymorphocellular reticulosarcoma. The Maximov cambial lymphocyte is assumed to be the most reliable cell source. The Willis teaching on tumor field holds good of the morphogenesis of follicular lymphomas. The problem of the differential diagnosis between follicular lymphomas and follicular reactive hyperplasia is discussed.