The objective of this study was to measure the frequency and severity of the behavioral effects of high-dose oral steroid therapy in children with nephrotic syndrome. We conducted a prospective assessment of the behavior of 12 children using a standardized psychological questionnaire at the time of diagnosis and again after 4 weeks of steroid therapy. A group of control children was also assessed. There was a significant increase in the total behavior score ( P=0.03) and specifically in aggressive and poor attention behavior items in the group of nephrotic children compared with the control group. Four of the children with nephrotic syndrome developed abnormal behavior in the clinical range compared with none of the controls. In conclusion, children with nephrotic syndrome treated with high-dose oral steroids are at risk of developing clinically relevant behavioral changes.