Introduction: Involvement of the central nervous system in patients with multiple myeloma is a rare event. We evaluated the diagnostic workup and prognosis of patients with leptomeningeal myelomatosis (LMM). Methods: Between April 2005 and April 2016, we identified 16 cases with LMM. The involvement was diagnosed by magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) cytology as well as flow cytometry. Fluorescence in situ hybridization (FISH) was used in 8/16 cases. In 1 case, genome-wide screening for genetic alterations using single-nucleotide polymorphism (SNP) array analysis was performed. Results: The median time from initial diagnosis until the occurrence of LMM was 434 days. At diagnosis, the median age was 60 years. The median cell count was 21/µL (range 1–1,333/µL). All CSF samples showed malignant pleocytosis, confirmed by flow cytometry in 12/16 patients. FISH revealed high-risk features in the majority of samples. Treatment for LMM consisted of intrathecal chemotherapy and radiation therapy. Genome-wide screening assays revealed different subclones. The outcome was dismal with a median overall survival after the diagnosis of LMM of 82 days. Conclusion: By combining several technical procedures, it is possible to identify most patients with LMM. Management of affected patients is challenging and the survival short after a diagnosis of LMM.