There are relatively few studies of the effect of retinoids on dermal tissue. A selective review of the literature reveals that when retinoids, especially all-trans-retinoic acid (tretinoin), are exposed to cultured human fibroblasts, they produce a marked reduction of fibroblast proliferation and collagen synthesis. Our clinical study of keloids and hypertrophic scars demonstrates in vivo effects of retinoids that are consistent with the in vitro data. Retinoids have significant clinical activity on dermal tissue, and further in vitro and in vivo development and testing of retinoids may lead to significant therapeutic advances in the treatment of fibrotic diseases.