Obesity is associated with an increased risk of certain cancers, including renal cell carcinoma. A possible mediator of this risk is insulin-like growth factor-1 (IGF-1). The authors evaluated the prognostic information of IGF-1, IGFBP-3, leptin, and prealbumin in sera sampled at diagnosis from 256 consecutive patients with renal cell carcinoma. Insulin-like growth factor-1 and leptin were positively correlated to body mass index (BMI). Insulin-like growth factor-1 and IGFBP-3 did not correlate to tumour stage or grade. Leptin and prealbumin were both inversely related to tumour stage and grade. When survival was analysed in patients with levels above a median of IGF-1, leptin, and prealbumin, prognosis was more favourable, compared with those with lower levels (p=0.017; p=0.024, and p<0.0001, respectively). In a multivariate analysis, tumour stage and serum IGF-1 levels were independent prognostic factors. The results indicate that serum IGF-1 at diagnosis is related to prognosis in renal cell carcinoma.