Numerous models have been developed to study polycystic ovarian syndrome in rats. In the present study, the syndrome was induced by exposure to constant light. The histological structure and differential distribution of extracellular matrix (ECM) fibers as well as the glycosaminoglycans (GAGs) content and composition of the ovarian follicular wall of rats with polycystic syndrome were evaluated. Histochemical differences were observed in the granulosa and theca externa of follicular cysts when compared to normal preovulatory follicles. The collagen content of the theca externa of follicular cysts, quantified by the picrosirius method, was higher than in the controls. The neutral carbohydrate and acidic GAG levels were lower in the granulosa and higher in the theca externa of cyst follicles than in control ovaries. Histomorphometrically, the follicular diameter was both a convenient and appropriate measurement for describing the cyst status; there were no differences in the thickness of each follicular layer. In conclusion, differences in the components of ECM were observed in the follicular wall of ovarian cysts compared with normal preovulatory follicles. However, since these changes did not occur uniformly in all layers of the follicular wall, their role in cyst development remains to be established.