Background We performed a retrospective nationwide study to explore age as a prognostic factor in synovial sarcoma patients.Methods Data on 613 synovial sarcoma patients were obtained from the Netherlands Cancer Registry. The prognostic relevance of age groups (children, adolescent and young adults (AYAs), adults, and elderly) was estimated by Kaplan-Meier survival curves and multivariable Cox-proportional hazards modelling.Results A total of 461 patients had localised disease at diagnosis. The 5-year overall survival (OS) was 89.3±4.6%, 73.0±3.8%, 54.7±3.6%, and 43.0±7.0% in children (n=54), AYAs (n=148), adults (n=204), and elderly (n=55), respectively. Treatment modalities had no significant effect on survival in the univariable analysis. Multivariable analysis identified age at diagnosis, tumour localisation, and tumour size as significant factors affecting OS. Both tumour localisation and size were equally distributed over the age groups.Conclusions We show that outcome of synovial sarcoma patients significantly decreases with age regardless of primary tumour site, size, and treatment.