Background: Few studies have characterized patients with smoldering multiple myeloma (SMM) in ethnically diverse settings and data regarding progression to multiple myeloma (MM) in real-world clinical populations is limited. Using data from a large healthcare system, we examined a contemporary cohort of adults with confirmed SMM and their progression to MM. Methods: We conducted a retrospective cohort study of SMM cases from 2010-2017 in Kaiser Permanente Northern California (KPNC). We used the KPNC SEER-based Cancer Registry to identify potential SMM cases by ascertaining MM cases with either: 1) “asymptomatic, evolving, or smoldering myeloma” status in the Cancer Registry or 2) mention of “smoldering” in clinical records. Chart review was conducted for potential SMM cases and confirmed SMM status was assigned using the 2014 IMWG criteria. SMM cases were followed for progression to MM and myeloma-directed therapy, excluding those with KPNC membership <1 year after diagnosis. Time to MM progression (or treatment) was examined. SMM cases were classified during follow-up as: a) SMM, no progression to MM (and no receipt of myeloma-directed therapy); b) SMM, progression to MM (and receipt of myeloma-directed therapy); and c) SMM, receipt of myeloma-directed therapy without frank progression to MM (follow-up was censored at treatment). Results: During 2010-2017, we identified 152 adults with confirmed SMM. The median age at diagnosis was 71 years (IQR, 62-78), 56% were male, and 55% were non-Hispanic White, 17% Black, 9% Hispanic, and 18% Asian. During follow-up, 28% of patients progressed to MM, with a median time to progression of 1.2 years (IQR 0.8-2.0). Over half (58%) did not progress during a median follow-up time of 3.4 years, and an additional 14% received treatment before a MM-defining event. Progression data by demographic group is shown in Table. Conclusions: This is one of the first studies to examine SMM progression in an ethnically diverse cohort using the 2014 IMWG criteria. Although follow-up time was limited, we found that over half of the identified SMM cases did not progress to MM. However, patients who did progress to MM generally required treatment within 2 years of SMM diagnosis. These findings support efforts to identify high-risk patients with SMM who may benefit from early initiation of therapy.