Intrauterine growth retardation (IUGR) resulting in a reduced number of nephrons is one of the nonimmune mechanisms that have been recently proposed as contributing to the progression of renal diseases. The purpose of our study was to determine whether IUGR has any effect on the clinical course and prognosis of IgA glomerulonephritis (IgA GN) in children. Fifty children with biopsy-proven IgA GN, who were followed for at least 3 years, were included. Six of the 50 children (12%) had signs of IUGR at birth, defined as birth weight below the 10th percentile for gestational age. There were no significant differences in initial clinical presentation between children with IUGR and those without IUGR. However, in kidney biopsy specimens, we found a significantly higher mean percentage of sclerotic glomeruli in children with IUGR than in those without IUGR (33 vs. 13%, p < 0.015). At the end of the follow-up period, we observed a significantly higher incidence of arterial hypertension in children with IUGR than in those without IUGR (50 vs. 11%, p < 0.05). Other differences between the two groups of children were not statistically significant. In conclusion, our study demonstrated an increased risk of the development of arterial hypertension and glomerulosclerosis in children with IgA GN who had suffered from IUGR with a birth weight below the 10th percentile for gestational age. IUGR may therefore help to identify early in the course of IgA GN those children who are at higher risk of an unfavorable course.