Aim. To investigate the relationship between concentration of lipoprotein(a) [Lp(a)] and the plasma level of the proprotein convertase subtilisin/kexin type 9 (PCSK9) in plasma of patients with severe hypercholesterolemia and various apolipoprotein(a) [apo(a)] phenotype. Material and methods. The study included 133 patients with plasma total cholesterol (TC) level above 7.5 mmol/L and/or low density lipoprotein cholesterol (LDL C)>4.9 mmol/L, previously not receiving lipid-lowering drugs. All enrolled patients have not clinical manifestations of coronary artery disease and significant carotid arterial lesions. Lipids, Lp(a), PCSK9 and apo(a) phenotype were determined for all patients. The concentration of LDL cholesterol (LDL Ccorr) was calculated according to the Friedwald’s formula with Dahlen’s modification, corrected for Lp(a) cholesterol. Results. Depending on the apo(a) phenotype, all patients were divided into three subgroups: the low molecular (LMW) apo(a) phenotype (n=37), the high molecular (HMW) apo(a) phenotype (n=47) and with the undetectable (ND) phenotype of apo(a) (n=49) due to the low plasma concentration of Lp(a) (mean level 5±2 mg/dL). The subgroups were comparable for all major clinical characteristics and lipids. The mean level of PCSK9 also did not differ between subgroups (ND apo(a) — 340±91, HMW apo(a) — 351±118 and LMW apo(a) — 344±103 ng/mL, p> 0.05). The Lp(a) concentration was significantly higher in patients with the LMW apo(a) phenotype compared to patients with LMW apo(a) phenotype (65±38 mg/dL and 32±28 mg/dL, p<0.05, respectively). In the general group the PCSK9 level correlated with the male (r=0.23, p<0.01) and age (r=0.21, p<0.05). We found a weak relationship between the Lp(a) and PCSK9 concentrations (r=0.19, p<0.05), which was enhanced in a subgroup with LMW apo(a) phenotype (r=0.45, p=0.005) and disappeared in HMW apo(a) phenotype (r=0.15, p=0.33). Lp(a) concentration (r=0.22, p=0.005) and male (r=0.18, p=0.04) adjusted for age, TC level and apo(a) phenotype were independent predictors of PCSK9 plasma level according to the results of multivariate regression analysis in the general patients group. Conclusion. The positive relationship between the concentrations of Lp(a) and PCSK9 is due to the presence of the low molecular weight apo(a) phenotype are illustrates the possible differences in metabolism and pathophysiological properties of Lp(a) with small and large apo(a) isoform.