Background: Multiple myeloma (MM) is the second most common hematologic malignancy. African Americans are more likely than Whites to be diagnosed with and die of MM, but they experience the same survival times in clinical trials, suggesting that differences in survival may be attributed to differences in receipt of treatment or differences in access to new treatments. We undertook this study to identify the reasons and needs underlying disparities in treatment among patients diagnosed with MM. Methods: We conducted in-depth interviews in 2019–2020 with patients diagnosed with MM between 2010 and 2014 who were identified as eligible for transplant and maintenance therapy and having experienced delays in or underuse of treatment for MM. Underuse was defined as the lack of a particular treatment that the patient was eligible to receive, not being transplanted if eligible, and/or not receiving maintenance therapy. Underuse included patients’ decision to delay harvest or autologous stem cell transplant (ASCT) for the time being and return to the decision in the future. All interviews were audio-recorded and transcribed verbatim. Four investigators independently coded transcripts through inductive analysis to assess reasons for treatment decisions. Results: Of the 29 patients interviewed, 68% experienced treatment underuse: 21% self-identified as African American, 5% as Hispanic, 10% as mixed race, 57% as White, and 16% as Asian. There were no racial differences in reasons for underuse or delay. Themes relating to treatment underuse included: perceived pros and cons of treatment, including potential harm or lack thereof in delaying treatment; physician recommendations; and personal agency. Conclusion: Patients’ decision making, delays, and underuse of MM treatment are influenced by social, personal, medical, and contextual factors. Patients consider their relationship with their physician to be one of the most significant driving forces in their decisions and treatment plans.