Zainel AAL, et al. - A total of 102,342 individuals aged between 18 and 65 years old with a valid serum vitamin D test result during the year 2017 were recruited by the researchers in order to examine the prevalence of vitamin D deficiency among individuals attending primary healthcare facilities in Qatar and to evaluate the correlation between vitamin D deficiency and some medical conditions in persons aged 18–65 years old. Among study individuals with no history of vitamin D replacement therapy in the prior months, the prevalence rate of severe vitamin D deficiency was 14.1%. The prevalence rate of vitamin D deficiency was as great as 71.4% and that of vitamin D insufficiency was up to 92.7%. None of the five chronic conditions investigated in the study (diabetes, hypertension, asthma, stroke and cardiovascular disease) had an understandable relationship with severe vitamin D deficiency status in bivariate analysis. Nevertheless, after adjusting for age, gender, body mass index, and nationality and each of the included chronic conditions, hypertension, cardiovascular diseases, and stroke put an individual at a greater risk of having a related severe vitamin D deficiency status. Hence, a higher prevalence of vitamin D deficiency among young adults, females, Qatari nationality and those with higher BMI was suggestive. Multivariate modelling demonstrated that hypertension, cardiovascular diseases, and stroke were related to a greater risk of severe vitamin D deficiency status.