OBJECTIVE: To ascertain whether vascular complications and high lipoprotein (a) [Lp(a)] concentrations are related in individuals with early-onset type 2 diabetes mellitus (T2DM). METHODS: This observational cross-sectional study included 591 individuals with early-onset T2DM who were divided into four groups based on Lp(a) values which was measured using immunoturbidimetry and presented as mg/dL: high, >50; intermediate, 30≤Lp(a)<50; low, 10≤Lp(a)<30; and very low, <10. The relationship between the risk of vascular complications and Lp(a) level was examined using a logistic regression model. RESULTS: The median age of onset for individuals with early-onset T2DM (n=591) was 37 years, duration of diabetes was 12 years, and glycated hemoglobin (HbA1c) level was 8.8%. The median Lp(a) was 10.40 (4.80-21.80) mg/dL, and Lp(a) concentration did not correlate with age, sex, or glycemic control (>0.05). Individuals in the low Lp(a) (OR=2.12, 95% CI 1.17-3.84, <0.05), intermediate Lp(a) (OR=2.76, 95% CI 1.10-6.98, <0.05) and high Lp(a) (OR=4.79, 95% CI 2.03-11.31, <0.01) groups had an increased risk of coronary heart disease (CHD) compared with those in the very low Lp(a) group after adjustment. Nevertheless, among individuals with early-onset T2DM, there was no correlation between Lp(a) concentration and the risk of cerebrovascular disease (CVL) and microvascular complications (>0.05). CONCLUSIONS: In patients with early-onset T2DM, Lp(a) concentration was independently associated with CHD. Lp(a) testing is essential to determine who has a latent high risk of CHD among patients with early-onset T2DM.