The aim of this study was to evaluate the effects of maternal malnutrition during lactation on prostate growth and estradiol serum concentration in the prostate of pups. At delivery, nine Wistar rats were separated into three groups: control group (C) with free access to a standard laboratory diet containing 22% protein; protein-energy-restricted group (PER) with free access to an isoenergy and protein-restricted diet containing 8% protein; and energy-restricted group (ER) receiving standard laboratory diet in restricted quantities, which were calculated according to the mean ingestion of the PER group. All pups were killed at weaning. PER and ER groups presented a significant reduction in estradiol serum concentration (C = 73.8 +/- 4.6, PER = 48.7 +/- 3.2, ER = 59.7 +/- 5.5 pg mL(-1), P < 0.01), total prostatic acini (C = 24 190.0 +/- 716.5, PER = 20 290.0 +/- 631.4, ER = 19 550.0 +/- 759.1 microm(2); P < 0.01), lumen of the prostatic acini (C = 5 590.0 +/- 165.4, PER = 3 776.0 +/- 251.3, ER = 4 658.0 +/- 198.1 microm(2); P < 0.01) and epithelial area of the prostate dorsal lobe (C = 18 120.0 +/- 391.4, PER = 16 520.0 +/- 799.2, ER = 14 890.0 +/- 589.8 microm(2); P < 0.01). Testosterone concentration was significantly increased only in the PER group when compared with the C group (C = 0.09 +/- 0.01, PER = 0.44 +/- 0.04, ER = 0.15 +/- 0.03 ng mL(-1), P < 0.001). An adequate nutritional state in early life is important for normal growth of the prostate gland, which seem to be related to serum levels of estradiol.