Vitamin D is essential for overall health, wellbeing, and the immune system. Hypervitaminosis D leads to many deleterious effects and increased mortality. This study was done to evaluate the effects of vitamin D toxic doses on histology and weight indices of some main immune system organs (spleen and thymus), and some organs that are prone to calcification due to hypervitaminosis D (liver, kidney, and heart) in rats. Thirty-five adult male Wistar rats were randomly assigned to four groups receiving water or vitamin D by oral gavage. The control group (8 rats) received distilled deionized water for 22 days. The experimental groups were low dose (LD, 9 rats, 1,500 IU of vitamin/rat/day for 21 days), intermediate dose (ID, 9 rats, 3,000 IU/rat/day for 22 days), and high dose (HD, 9 rats, 6,750 IU/rat/day for 22 days). No other studies used such high doses on rats. Compared to the control group, the mean liver and kidney indices for the ID group were both significantly lower, while the mean heart index for the LD group was significantly higher. The spleen and thymus indices were not significantly different. Histopathology of the organs showed minimal changes for the LD group while the ID and HD groups had focal degenerative changes in the liver and more so in the kidney. Lymphocytes were decreased in both the spleen and thymus parenchyma. In conclusion, the higher doses of vitamin D had toxic effects on the organs studied and thus affected the immune system and health in general.