OBJECTIVE - To evaluate the effect of glycemic control improvement with insulin therapy on lipoprotein(a) [Lp(a)] levels in patients with NIDDM. RESEARCH DESIGN AND METHODS - We performed a longitudinal study in a tertiary referral center to compare lipid and Lp(a) levels before and after 3 months of insulin therapy in 60 poorly controlled NIDDM patients (32 men, 28 women). Patients previously treated with oral hypoglycemic agents (n = 50) received one to two insulin doses, and those previously treated with insulin (n = 10) received multiple insulin doses. Lp(a) levels were measured by the Terumo method. Differences between the two periods were assessed by the paired t test and Wilcoxon's test. RESULTS - After 3 months of insulin therapy, HbA(1c) decreased from 9.6 ± 1.9 to 6.0 ± 1.4% (P < 0.0005) in all patients and from 9.1 ± 2.1 to 6.1 ± 2.9% (P < 0.05) in patients under multiple insulin doses, being ≤6.0% in 59% of patients. Total triglyceride and VLDL cholesterol levels decreased (P < 0.01) and HDL cholesterol increased significantly (P < 0.0005). However, no changes in Lp(a) levels were observed in all patients (25.3 ± 25.0 vs. 25.7 ± 27.2% mg/dl) and in patients with baseline Lp(a) levels above (63.5 ± 15.5 vs. 65.1 ± 23.1 mg/dl) or below 30 mg/dl (11.5 ± 7.5 vs. 11.5 ± 7.3 mg/dl). In addition, patients reaching HbA(1c) levels ≤6.0% or >6.0% presented similar Lp(a) levels (26.0 ± 29.1 vs 25.3 ± 25.0 mg/dl). Moreover, no correlations were observed between changes in Lp(a) levels and in the glycemic control parameters. CONCLUSIONS - This study shows that the improvement of glycemic control by insulin therapy does not influence plasma Lp(a) levels, measured by the Terumo method, in NIDDM patients, independently of baseline values and the degree of glycemic control reached.