In this study, we investigated the morphometric and histological alterations of the aorta, brachial, and femoral arteries in 4- and 20-week-old rats that were prenatally exposed to diclofenac sodium (DS). For this purpose, pregnant rats were divided into three groups: control, saline injected, and drug treated. Beginning from day 5 after mating through day 15 of pregnancy, saline or DS (1 mg/kg daily) was intraperitoneally injected into groups 2 and 3. No injection was given to the rats in the control group. After spontaneous delivery, male offspring were obtained. At the end of weeks 4 and 20, vessel samples were removed. After dissection and routine histological preparation, histopathological and stereological investigations were made. Our results indicate that both saline and DS application lead to a decrease in the mean volume fraction of tunica media in all vessel walls, but result in an increase of the same fraction of lumen to the whole vessel wall, especially in 4-week-old rats. Elastic fibers of the vessel wall were affected by DS treatment, because a decrease of the elastic fiber was observed in this group. Finally, in light of our findings, we suggest that DS or saline may lead to vascular changes (i.e., vasodilatation or vasoconstriction) in rats that are prenatally subjected to increased volume of maternal blood resulting from injection.