['Serum 25-hydroxyvitamin D [25(OH)D] concentration has been inversely associated with the prevalence of metabolic syndrome (MetS), but the relationship between 25(OH)D and incident MetS remains unclear.', 'We evaluated the prospective association between 25(OH)D, MetS, and its components in a large population-based cohort of adults aged 25 yr or older.', 'We used baseline (1999-2000) and 5-yr follow-up data of the Australian Diabetes, Obesity, and Lifestyle Study (AusDiab).', 'Of the 11,247 adults evaluated at baseline, 6,537 returned for follow-up. We studied those without MetS at baseline and with complete data (n = 4164; mean age 50 yr; 58% women; 92% Europids).', 'We report the associations between baseline 25(OH)D and 5-yr MetS incidence and its components, adjusted for age, sex, ethnicity, season, latitude, smoking, family history of type 2 diabetes, physical activity, education, kidney function, waist circumference (WC), and baseline MetS components.', 'A total of 528 incident cases (12.7%) of MetS developed over 5 yr. Compared with those in the highest quintile of 25(OH)D (≥34 ng/ml), MetS risk was significantly higher in people with 25(OH)D in the first (<18 ng/ml) and second (18-23 ng/ml) quintiles; odds ratio (95% confidence interval) = 1.41 (1.02-1.95) and 1.74 (1.28-2.37), respectively. Serum 25(OH)D was inversely associated with 5-yr WC (P < 0.001), triglycerides (P < 0.01), fasting glucose (P < 0.01), and homeostasis model assessment for insulin resistance (P < 0.001) but not with 2-h plasma glucose (P = 0.29), high-density lipoprotein cholesterol (P = 0.70), or blood pressure (P = 0.46).'] Is low serum 25-hydroxyvitamin D associated with increased risk of the development of the metabolic syndrome at five years : results from a national , population-based prospective study ( The Australian Diabetes , Obesity and Lifestyle Study : AusDiab )?