Background: In this study, we investigated the effect of calcium and vitamin D (Ca/Vit D) supplementation on the clinical, hormonal, and metabolic profile of patients with low vitamin D levels. In addition, we investigated the effect of Ca/Vit D supplementation on asymmetric dimethylarginine (ADMA) level in patients with polycystic ovary syndrome (PCOS). Methods: In total, 75 patients aged 19–35 years, with a normal body mass index and a diagnosis of PCOS and Vit D deficiency/insufficiency, were included in the study. Patients received 50,000 IU of vitamin D3 once a week for 8 weeks. Afterward, 2500 mg calcium carbonate equivalent to 1000 mg calcium ion and 9.68 mg cholecalciferol equivalent to 880 IU vitamin D3 were administered orally as a maintenance treatment once a day. Results: The mean age of the patients was 21.7 ± 3.5. After Ca/Vit D supplementation, Vit D levels significantly increased compared to baseline (8.6 ng/ml) levels. An increase in SHBG levels (p < 0.001), a decrease in total testosterone, FAI (p = 0.042), and ADMA levels (p < 0.001) were observed in the first and third months compared to the onset. Significant improvement compared to baseline was observed in menstrual irregularity and median mFG score. Conclusion: Ca/Vit D supplementation can improve PCOS symptoms such as menstrual dysfunction, hirsutism, and hyperandrogenism. It may be effective in reducing the risk of cardiovascular disease in patients with PCOS later in life by decreasing ADMA levels, which is an indicator of endothelial dysfunction.