Abstract Purpose Sinonasal mucosal melanoma (SNMM) is a rare malignancy, characterised by high (local) recurrence rates and poor survival. Comprehensive understanding of tumour etiology is currently lacking, which complicates adequate tumour treatment. Besides examining trends in incidence, this study aims to assess the association between clinical characteristics, treatment practices and patient outcomes, with the objective of establishing a baseline from which SNMM management can be enhanced. Methods All newly diagnosed SNMM cases in The Netherlands between 2001 and 2021 were included using data from The Netherlands Cancer Registry (NCR). Results A total of 320 patients were included. The annual incidence rate for the overall population was stable over the inclusion period with an annual percentage change (APC) of only − 0.01%. The 5-year overall survival (OS) and relative survival (RS) were 24.5 and 32.4%, respectively. Relative survival did not increase over time. The addition of adjuvant radiotherapy to surgery was not associated with a higher OS and RS compared to surgery alone. Conclusion Sinonasal mucosal melanoma is a rare disease with stable incidence rates in the Netherlands between 2001 and 2021. There has been no improvement in survival over the course of the inclusion period. The study reaffirms that adjuvant radiotherapy does not seem to improve patient outcomes. Given the generally poor outcomes for SNMM patients, novel therapeutic options ought to be considered in order to improve care.