Progastrin-releasing peptide (proGRP) is a recently identified biomarker of small-cell lung cancer. In well-differentiated neuroendocrine tumours (WDNETs), this study investigates the association between proGRP and tumour characteristics and the prognostic value of proGRP levels compared with chromogranin A (CgA) levels.Serum samples were obtained in 282 patients with WDNET. The receiver operating characteristic (ROC) curve technique was used to assess specificity and sensitivity in the identification of a primary tumour location. Cox proportional hazards models and Kaplan-Meier curves were constructed to determine the association of patients' characteristics and tumour markers with survival.For proGRP, the ROC curve indicated a cut-off level of 90 ng/l (approximately twice the upper reference value), with a specificity of 99% and a sensitivity of 43% in distinguishing primary pulmonary tumours from other sites. In the multivariate Cox model, both proGRP and CgA were strongly associated with survival (P < 0.0001 for both variables).A high-risk proGRP level (more than twice the upper reference value) in patients with WDNETs is a strong indication for a primary tumour in the lung. Besides CgA, proGRP is a complementary tumour marker for prognosis and treatment monitoring in patients with neuroendocrine tumour.