Obesity is a risk factor for incident asthma in adults, and obesity is a major component of metabolic syndrome. This study aimed to explore the associations of metabolic syndrome and its components with the cumulative incidence of asthma in adults. We conducted a prospective cohort study of participants who were asthma-free at baseline (n = 23 191) in the Nord-Trøndelag Health Study from 1995 to 2008. Baseline metabolic syndrome was categorised using the definition of the Joint Interim Statement from several international organisations. Incident asthma was self-reported at follow-up, which averaged 11 years. Metabolic syndrome was a risk factor for incident asthma (adjusted OR 1.57, 95% CI 1.31-1.87). This association was consistent in sensitivity analyses using a stricter asthma definition (adjusted OR 1.42, 95% CI 1.13-1.79). Among the components of metabolic syndrome, two remained associated with incident asthma after mutual adjustment for the other metabolic components: high waist circumference (adjusted OR 1.62, 95% CI 1.36-1.94) and elevated glucose or diabetes (adjusted OR 1.43, 95% CI 1.01-2.04). Metabolic syndrome and two of its components (high waist circumference and elevated glucose or diabetes) were associated with an increased risk of incident asthma in adults.