© 2022, International Osteoporosis Foundation and National Osteoporosis Foundation.Summary: Vitamin D deficiency is still an important subject due to its significant effects on various tissues and functions. We found a relationship between vitamin D deficiency and increase in adipose tissue thicknesses. This situation reveals the importance of vitamin D supplementation, the harms of weight gain and obesity, and the importance of a balanced diet. Purpose: Although the relationship between vitamin D (VitD) levels with body composition and physical/cognitive functions have been investigated in various studies, however, there is no study evaluating all these parameters together. In accordance with, we aimed to evaluate the relationship between VitD deficiency with body composition (i.e., skin, subcutaneous fat, and muscle thicknesses) and physical/cognitive functions. Methods: A total of 203 adults (78 M, 125 F, aged 19–91 years) who had recent 25-OH-vitamin D measurements were included. Ultrasonographic (US) measurements (skin, subcutaneous fat, and muscle thicknesses) were made from the dorsum of the hand, and anterior sides of forearm, arm, and thigh. Handgrip strength, gait speed, Timed Up and Go Test, and Chair Stand Test were evaluated. Additionally, cognitive status was also evaluated with Mini-Mental State Exam. Results: Subjects were classified as VitD deficient group (< 20 ng/ml, N = 125) and control group (≥ 20 ng/ml, N = 78). The groups were not significantly different as regards age, gender, and anthropometric measurements (all p > 0.05). Subcutaneous fat tissues were thicker in the VitD deficient group (all p < 0.05). All the other US measurements and functional/cognitive tests were not significantly different between the groups (all p > 0.05). According to linear regression analyses, body mass index (BMI) was independently related with all subcutaneous fat thicknesses in both genders, and VitD deficiency was related with all subcutaneous fat thicknesses in females and anterior forearm subcutaneous fat thickness in males (all p < 0.05). Conclusion: We imply that together with BMI, VitD deficiency is independently related with increased regional subcutaneous fat tissue. We also underscore the role of US measurements for evaluation of body composition in related clinical scenarios.