Background: Long non-coding RNAs are implicated in metabolic diseases and malignancies, but their role in multiple myeloma (MM) with type 2 diabetes mellitus (T2DM) remains unclear. This study evaluated Long non-coding RNA Morrbid expression in MM patients with/without T2DM. Methods: The study enrolled 107 MM patients (48 with T2DM, 59 without) and 72 non-MM controls (23 with T2DM, 49 without). Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood samples using red blood cell lysis. Total RNA was extracted from PBMCs, followed by reverse transcription, and the expression levels of Morrbid were detected by Reverse transcription-quantitative PCR. Results: We found that the expression of Morrbid was upregulated in the MM group compared to the non-MM patients. Within the MM group, the expression of Morrbid was significantly higher in patients with T2DM than in those without T2DM. In contrast, no significant difference in Morrbid expression was observed between T2DM and non-T2DM patients in the non-MM patients. Furthermore, we discovered a positive correlation between Morrbid expression and fasting blood sugar levels in MM patients. Operating characteristic curve analysis revealed an area under the curve of 0.822 (sensitivity 77.1%, specificity 79.7%) for diagnosing T2DM in MM, suggesting that Morrbid may serve as a novel diagnostic biomarker for T2DM in MM patients. Conclusions: The high expression of Morrbid in MM patients with T2DM may indicate its critical role in tumor-related glucose metabolism. Additionally, Morrbid may potentially serve as a diagnostic biomarker for T2DM in MM patients.