BACKGROUND: Trabectedin was in Europe approved for treatment of metastatic soft tissue sarcoma (STS) in 2007 based on results of a phase II study with relatively few patients. The purpose of this nationwide retrospective study was to assess efficacy and safety of using trabectedin in the entire unselected cohort of patients with metastatic sarcoma and to test known, as well as new prognostic factors that may affect overall survival (OS). PATIENTS AND METHODS: Between January 2008 and April 2013, 117 patients were treated with trabectedin for metastatic sarcoma in the three specialized sarcoma centers in Denmark. Known prognostic factors such as age, gender and performance status, the histopathology as well as other new factors such as response to previous chemotherapy and hyponatremia were tested. RESULTS: Median age was 59 years. Lipo- and leiomysosarcomas (L-sarcomas) represented 43% of the cases and 18% had hyponatremia before the start of trabectedin. The median number of previous lines of chemotherapy was two (range 0-6) and the median number of chemotherapy cycles given before trabectedin was nine (range 0-85). The median number of trabectedin cycles was three (range 1-17). The median OS for the whole cohort was seven months. Poor performance status, non-L-sarcomas, and hyponatremia were statistically significant adverse prognostic factors with median survival of: 4, 5, and 2 months compared to 9, 12 and 13 months, respectively. Moreover, having achieved clinical benefit [complete response (CR), partial response (PR) or stable disease (SD)] from previous chemotherapy was a favorable prognostic factor for response to trabectedin. In multivariate analysis hyponatremia was the only independent significant poor prognostic factor affecting OS. CONCLUSIONS: This retrospective study confirmed the previously published safety and efficacy of trabectedin in patients with metastatic sarcoma and showed hyponatremia to be a strong independent statistically significant poor prognostic factor.