Aim: The aim of this study was to investigate the incidence of vitamin D deficiency and to demonstrate its influence on the hormonal parameters of fertility and on pregnancy in women undergoing in vitro fertilisation. Moreover, we aimed to determine whether there are differences in vitamin D status between women suffering from endometriosis, polycystic ovary syndrome and hypothyroidism as frequent causes of infertility. Materials and Methods: The study included 66 patients who were undergoing in vitro fertilisation at the Institute for Gynecological Endocrinology and Human Reproduction of the Clinic for Female Diseases and Birth of KBC Split. The data on the values of sex hormones and vitamin D, anthropometric measures as well as data on pregnancy have been collected retrospectively. Depending on the causes of infertility, the patients were divided into 4 groups: women with no female disease as the cause of infertility (control group), women with endometriosis, hypothyroidism and PCOS, and pregnant and non-pregnant women. Results: Average vitamin D values were 57.7±22.2 nmol/L, and 78.8% had vitamin D deficiency. Vitamin D differed between summer and winter part of the year (p = 0.007), while AMH did not show this diference for all subjects in total (p = 0.864), but in the control group it has shown the trend toward it (p = 0.058). The correlation of vitamin D with each hormone did not show any statistical significance: FSH (p = 0,209), LH (p = 0,700), AMH (p = 0,827), estradiol (p = 0,548), testosterone (p = 0,965), progesterone = 0.239), TSH (p = 0.374), prolactin (p = 310). The status of vitamin D did not differ between the control group and the group of women suffering from endometriosis (p = 0.896), hypothyroidism (p = 1.0) and PCOS (p = 0.599). There was also no difference in the status of vitamin D between the women who were pregnant and those who were not (p = 0.530) as same as there was no evident association with smoking (p = 0.066) and body mass index (p = 0.618). As random findings, we found that women who smoke had lower prolactin (p = 0.042) and higher AMH (p = 0.027). Conclusion: Vitamin D correlation did not reach statistical significance for any observed parameter. Therefore in our research we can conclude that vitamin D does not play a major role in the treatment of infertility or in the pregnancy achievement. The results of many world studies do not show unambiguous results, but most of them are in favor of significant benefits of vitamin D in the treatment of PCOS, IVF outcomes and clinical pregnancy, but also in the prevention of fetal anomalies and numerous pathological conditions in pregnancy. In this respect, it makes sense to compensate for vitamin D deficiency because it is inexpensive, easy to use and safe, and although it has not had an impact on achieving pregnancy, it has influence of affecting its more favorable course as well as health in general.