The Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) share similar molecular characteristics in that they frequently harbor hotspot mutations in JAK2, CALR or MPL, leading to activated JAK/STAT signaling. However, these MPN have distinct symptoms, morphology, and natural histories, including different tendencies to progress to fibrosis. Although the role of inflammation in tissue fibrosis is well recognized, inflammatory gene expression in bone marrows involved by MPN has been understudied. We analyzed the expression of inflammatory genes by directly measuring RNA transcript abundance in bone marrow biopsies of 108 MPN patients. Unsupervised analyses identified gene expression patterns that distinguish prefibrotic (grade 1-2) MPN from overtly fibrotic (grade 2-3) MPN with high sensitivity and specificity in two independent cohorts. Furthermore, prefibrotic and overtly fibrotic MPN are separable into subsets with different activities in biological pathways linked to inflammation, including cytokines, chemokines, interferon response, and toll-like receptor signaling. In conclusion, this study demonstrates that MPN with overt fibrosis is associated with significant inflammatory gene upregulation in the bone marrow, revealing potential roles for multiple pro-inflammatory signaling networks in the development of myelofibrosis and suggesting potential therapeutic mechanisms to alleviate this process in the bone marrow microenvironment.