Background. Ferritin is a high molecular weight protein which reflects body iron stores, but may also rise in the case of an acute phase response. Recently, ferritin has been identified as a predictive factor in the development and progression of atherosclerosis. This is the first report on serum ferritin levels in patients with proteinuria. Methods. We have analysed the data of 142 male patients with a glomerular disease, and proteinuria exceeding 1 g/day. In all patients, we measured various parameters related to proteinuria, serum ferritin and serum iron. Serum β2-microglobulin and the Modification of Diet in Renal Disease (MDRD) equation were used as measures of the glomerular filtration rate (GFR). Results. Mean age (±SD) was 46±15 years, MDRD-GFR 57±25 ml/min/1.73 m2 and median proteinuria 8.0 g/day [interquartile range (IQR) 3.6–13]. Serum albumin (29±9 g/l) and transferrin levels (1.7±0.5 g/l) were low, and cholesterol levels were elevated (median 7.3, IQR 5.9–9.5 mmol/l). Median serum ferritin was 148 µg/l (IQR 89–282), and exceeded 280 µg/l, the upper limit of normal, in 36 patients (25%). Elevated serum ferritin levels could not be explained by an acute phase response as determined by C-reactive protein, or haemochromatosis (DNA analysis). Regression analysis showed an independent relationship between ferritin levels and serum cholesterol, GFR and serum transferrin. Conclusions. Serum ferritin levels are elevated in patients with overt proteinuria. The independent negative relationship between serum ferritin and transferrin points to a specific process and suggests that increased production of ferritin may compensate for the loss of the iron-binding protein transferrin, thus reducing the amount of free iron. Further studies are needed to elucidate the role of ferritin in patients with proteinuria, especially because of the suggested association between ferritin and atherosclerosis.