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Current diagnostic tests cannot differentiate the majority of prostate cancers with a low likelihood of progression from the minority with more aggressive potential. We examined whether the measures of vitamin D were associated with prostate-specific antigen (PSA) doubling time in men undergoing active monitoring. We examined the associations of circulating 25-hydroxyvitamin D (25(OH)D), 1,25-dihydroxyvitamin D (1,25(OH)2D), and vitamin D pathway polymorphisms with PSA doubling time in 490 men undergoing active monitoring for localized prostate cancer within a UK population-based cohort study [mean follow-up 4.4 years (range: 0.3–7.6)]. Repeat PSA measurements were analyzed using multilevel models. There was no evidence that circulating 25(OH)D levels, 1,25(OH)2D levels, or vitamin D pathway polymorphisms were associated with postdiagnosis PSA doubling time. Stratifying the results by prostate cancer grade at diagnosis (high grade or low grade) did not alter the results. We found no evidence that either circulating 25(OH)D, 1,25(OH)2D, or vitamin D pathway polymorphisms were associated with PSA doubling time in men undergoing active monitoring for localized prostate cancer. Future studies should examine the associations of variation in vitamin D with clinical outcomes (metastases and death).