Aim of research: To analyze the correlation between the degree of expression of alpha-smooth muscle actin (ASMA) in glomeruli and interstitium with independent prognostic factors (MEST score) that were identified in the Oxford classification of IgA nephropathy in the year 2009. Research structure: Retrospective cross-sectional study. Study site: Department of Pathology, Forensic Medicine and Cytology, Split University Hospital. Participants: Patients with IgA nephropathy that were analyzed for immunohistochemical expression of ASMA and whose MEST score in the original histological preparations was determined. Main outcome measures: Interstitial ASMA expression correlation with prognostic factors from the Oxford classification and glomerular filtration. Results: The intensity of ASMA expression in the renal interstitium was significantly associated with mesangial hypercellularity (P=0,03) and segmental glomerulosclerosis (P=0,01). ASMA expression in glomeruli and interstitium was not associated with the degree of tubular atrophy/ interstitial fibrosis (P=0,78 and P=0,89). There is a statistically significant correlation between the degree of expression of ASMA in the interstitium and age (P=0,001). Significant differences in the level of expression of ASMA in the interstitium between the various renal syndrome were determined (P=0,09). ASMA expression in the interstitium is associated with serum creatinine (P=0,001) and negatively correlated with the value of creatinine clearance (P=0,01). There was no significant correlation between biuret and ASMA expression in glomeruli and interstitium (P=0,53 and P=0,11). ASMA expression in glomeruli and interstitium is not associated with systolic (P =0,35 and P=0,22) and diastolic pressure (P =0,13 and P=0,19). Conclusions: Higher expression of ASMA in the interstitium is significantly correlated with unfavorable prognostic indicators from Oxford classification (M1, S1) and is associated with a reduction in glomerular filtration rate.