Background Proteinuria has been recognized as a marker of systemic inflammation and endothelial dysfunction associated with insulin resistance and β-cell impairment, which can contribute to the development of type 2 diabetes mellitus (T2DM). However, it is unknown whether the dipstick proteinuria test has a predictive value for new-onset T2DM. Methods This retrospective cohort study analyzed 239,287 non-diabetic participants who participated in the Korean nationwide health screening program in

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... 009–2010. Proteinuria was determined by the urine dipstick test at the baseline health screening. We performed multivariate Cox proportional regression analyses for the development of new-onset T2DM. Follow-up was performed until December 2015. Results During the mean follow-up period of 5.73 years, 22,215 participants were diagnosed with new-onset T2DM. The presence of proteinuria was significantly associated with an increased risk of T2DM (adjusted hazard ratio: 1.19, 95% confidence interval: 1.10, 1.29). There was a positive dose–response relationship between the degree of dipstick proteinuria and T2DM risk. This significant association between proteinuria and T2DM risk was consistent regardless of the fasting glucose level at baseline. Conclusions Dipstick proteinuria is a significant risk factor for new-onset T2DM. Therefore, proteinuria might be a useful biomarker to identify those at a high risk for developing T2DM.