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Background: Serum 25-hydroxyvitamin D (25(OH)D) assays have become readily available in India over the past decade. A large number of cross-sectional studies have been performed on the vitamin D status and the prevalence of vitamin D deficiency (VDD) in India. However, seasonal and long-term trends in serum 25(OH)D levels have been reported less frequently. Aim: To determine the seasonal and year-wise variation in vitamin D status at a tertiary care hospital in north India. Materials and Methods: Using hospital records, the data on serum 25(OH)D assays performed in its endocrinology laboratory between 2008 and 2016 were obtained. For analysis of seasonal trends, the months of a year were divided into following seasons: March to June (summer season), July to October (rainy season), and November to February (winter season). VDD was defined as serum 25(OH)D concentration ង ng/mL. Results: A total of 26,339 assays of serum 25(OH)D were analyzed in the study. The year-wise assay numbers increased steadily from 2008 to peak in the year 2012, followed by a decline and a second smaller peak in the year 2016. The mean serum 25(OH)D concentration increased from 19.1 ± 16.4 ng/mL in 2008 to 21.7 ± 17.1 ng/mL in 2016 (P = 0.02). Between 2008 and 2016, the prevalence of VDD decreased from 71.9% to 54.3% in females, and from 56.7% to 52.1% in males. The levels in rainy season were significantly higher as compared to winters and summers (P < 0.05 for both). Hypervitaminosis D (serum 25(OH)D >100 ng/mL) and vitamin D toxicity (serum 25(OH)D >150 ng/mL) were seen in 319 (1.2%) and 27 (0.1%) assays, respectively. Conclusions: This study provides data on seasonal and year-wise trends in vitamin D status over a long period of time at a tertiary care hospital in north India. A long-term trend toward improving vitamin D status, especially in females, was noted in the study. The prevalence of VDD was found to decrease in the analyzed samples during the study period. [ABSTRACT FROM AUTHOR]