BACKGROUND This study was conducted to develop a histology-specific nomogram to predict postoperative overall survival (OS) at 5 and 10 years in primary retroperitoneal soft tissue sarcoma (STS). METHODS Data registered at a single institution (National Cancer Institute, Milan, Italy) prospective sarcoma database were used. In the present analysis, patients with primary localized retroperitoneal STS resected with curative intent between 1985 and 2007 were included. A parametric piecewise exponential survival multivariate model was used for nomogram development, and internal validation was performed with standard methodologies. Known prognostic variables, such as age, tumor burden, histologic variant (as reviewed by a sarcoma pathologist), grade, and surgical margins were considered as putative predictors. RESULTS Among the 192 patients analyzed, within 10 years from surgery, 114 patients were alive, with a median follow-up time of 55 months (interquartile range, 25-104 months). Among the investigated factors, only histologic subtype did not reach significance at the 10% level. The relative hazard increased while increasing tumor size up to about 25 cm, and decreased thereafter. CONCLUSIONS A histology-specific nomogram for retroperitoneal STS is now available. It can be used for better assessing the risk of the single patient and then making individualized decisions within the specific subset of retroperitoneal sarcomas. Cross-check external validation should be performed.