Background: Multiple myeloma (MM) is a disease predominantly of older adults with an average age of 69 at diagnosis. Limited data is available on the diagnostic details and outcomes of MM patients ≤50 years old, and particularly how these trends have changed over the past two decades. We present data from one of the largest retrospective cohorts of younger MM patients. Methods: This retrospective review identified 213 MM patients by pooling two datasets: 88 MM patients aged ≤50 years at first stem cell transplant (SCT) between 1/1/2000-6/1/2021 at University of California (UC), San Diego; and 125 MM patients age ≤50 years old at diagnosis between 1/1/2014-7/1/2021 at UC Davis. Demographics, diagnostic details, treatment, response, and overall survival (OS) data were collected. Results: The pooled dataset included 209 patients with MM and 4 with plasma cell leukemia. The median age was 45, with 58 (27%) Hispanic and 37 (17%) Black patients. In 89 patients with available data, 23% were R-ISS-1, 58% were R-ISS-2, and 19% were R-ISS 3. Overall, 14% of patients had high-risk cytogenetics [t(4;14),del17p, or t(14;16]]. Patients diagnosed and treated in 2000-2010 were more likely to have received doublet or cytotoxic chemotherapy for induction therapy, while 80% of patients in 2010-2021 received triplet-based therapies. Responses to induction improved across decades, with 23% of patients in the earlier cohort vs 49% patients in the later cohort achieving a very good partial response (VGPR) or better. Eighty-five percent of patients received a SCT, the majority being autologous with only 13 upfront or salvage allogeneic SCTs in the earlier and 1 in the later cohort. The median OS for the entire cohort is 168 months, 171 months in the early cohort, and not reached in 2011-2021 cohort. Conclusions: We present retrospective data of a large and diverse cohort of California MM patients ≤50 years old, with nearly 50% of patients from underrepresented populations spanning over 2 decades. We found similar diagnostic features and risk group to those reported in the general MM population. Noticeable improvements in treatment responses were seen in the later decade with the introduction of modern therapies. A median OS of 14 years for the entire cohort over 20 years offers a glimpse into the hopeful promise for extended survival of younger patients as more effective therapies lead to deeper and more durable responses.