Clinical observations show that two subtypes of sinonasal malignant melanoma exist: uni- and multilocular melanoma. The aim of this retrospective study was to determine the prevalence and outcome of multilocular sinonasal malignant melanoma. All patients with sinonasal malignant melanoma treated at our institution between 1992 and 2011 were included. Survival and recurrence data were analyzed related to the distribution pattern of the tumors and other factors. Twenty-five patients were identified and included in the analysis. Seven patients (28 %) suffered from multilocular, the remaining 18 patients (72 %) from unilocular sinonasal malignant melanoma. The first group showed a significantly worse disease-free survival, whereas disease-specific and overall survival did not differ between the two subtypes. Multilocular sinonasal malignant melanoma is associated with an unfavorable disease-free survival compared to its unilocular counterpart.