Clinical and animal studies have shown a higher risk of an aggravated course of renal disease in childhood after birth for babies small for gestational age (SGA). In addition relative "supernutrition" and fast weight gain in early infancy seem to support the development of later disease. In a retrospective analysis of 62 cases of idiopathic nephrotic syndrome treated between 1994 and 2004 at a university centre for paediatric nephrology, we related the course of disease to birth weight and to the weight gain in the first 2 years of life. Six children were born SGA (birth weight <-1.5 standard deviation score), and 56 were born as appropriate for gestational age (AGA). In all SGA children renal biopsy was performed, while only 55% of the AGA children underwent renal biopsy (P = 0.07), showing no difference in renal histology. In the SGA group, four of six patients developed steroid resistance (vs 12/56 AGA, P < 0.05). Of the SGA children, 83% needed antihypertensive treatment in the course of the disease compared to 39% of the AGA children (P = 0.07). The extent of weight gain between birth and 24 months of age did not influence the course of disease. In conclusion, we were able to find evidence for an aggravated course of idiopathic nephrotic syndrome in former SGA children. Independently of birth weight, weight gain in the first 2 years of life did not influence the course of disease.