Background: Vitamin D was found to be linked with many derangements in the human body. Its association with menstrual irregularities has been significantly reported. 
Objective: Evaluation of the association between vitamin D deficiency and menstrual irregularities.
Study design: This cross- sectional study was conducted from March 2023- August 2023 at the outpatient clinic of a tertiary hospital. We recruited women presented with menstrual irregularities according to predetermined inclusion and exclusion criteria. A control group of women with regular cycles was included. Vitamin D level was evaluated in both groups. 
Results: This study recruited 104 women (52 participants per group). Vitamin D deficiency was noted in 46/104 participants (44.2%). Women with menstrual irregularities were younger than those with regular cycles (p-value 0.0001). The menstrual cycle length differed significantly between both groups (p-value 0.0001). Vitamin D level was significantly lower in the study group than in the control group (20.0 ± 11.9 and 28.7 ± 16.6, respectively, p-value 0.003). Younger age was a significant predictor for irregular cycles (p-value 0.005).
Conclusion:  Vitamin D deficiency was noted significantly among women with irregular cycles. Age was a significant predictor for irregular cycles rather than vitamin D levels.