Objective: To examine time- and dose-dependent association of statin use with developing incident diabetes in primary-prevention patients. Methods: Using the national health insurance data, our study comprised a cohort of adults aged 40 years or older with hypercholesterolemia who would be eligible for statin therapy and without a history of ASCVD between 2005 and 2012. The primary outcome was the occurrence of clinically relevant diabete. Propensity-score matching was used to identify a cohort of patients with similar baseline characteristics between statin user and non-user group. We assessed the association of statin use with the risk of new-onset diabetes, according to the duration, potency, and cumulative dose of statin therapy. Results: Among 2,162,119 adults with hypercholesterolemia who might be eligible for statin therapy, 638,625 (29.5%) ever received statin and 1,523,494 (70.5%) never used statin. With the use of propensity-score matching, 518,491 patients in the statin user group were matched with 518,491 patients in the statin non-user group. During average follow-up of 3.9 years, ever use of statin was associated with diabetes risk (13.4 and 6.9 per 1,000 person-years, respectively; adjusted hazard ratio [HR], 1.88; 95% confidence interval [CI], 1.85- 1.93). There was a trend toward excess risk of diabetes associated with increasing duration of statin use (HR 1.25 for less than 1 year, HR 2.22 for 1-2 years, and HR 2.62 for more than 2 years), with a higher intensity of statin (HR 1.75 for low or moderate potency and HR 2.31 for high potency), and with increasing cumulative dose of statin (HR 1.06 for low tertile, HR 1.74 for middle tertile, and HR 2.52 for high tertile of defined daily disease). Conclusion: Among adults receiving statin therapy for primary prevention, there was time- and dose-dependent association of statin use with increased risk of new-onset diabetes.