Background: Obesity has been implicated as a risk factor for the development of certain types of cancers, including multiple myeloma. Previous studies in other tumor types suggest that overweight subjects may have better outcomes, however, in relapsed/refractory multiple myeloma (RRMM), it is unknown whether body weight affects outcomes to therapy. Methods: We conducted a retrospective analysis of 13 RRMM clinical trials submitted to the FDA between 2012-2018. Patients were divided into four groups, underweight (BMI < 18.5 kg/m²), normal weight (BMI 18.5- < 25 kg/m²), overweight (BMI 25.0- < 30 kg/m²) and obese (BMI > 30.0 kg/m²). A multivariate analysis for progression free survival (PFS) and overall survival (OS), stratified by study and adjusted for age, cytogenetic risk group (Standard, High, Unknown), immunoglobin subtype (IgG Y/N), ECOG status (0-1, > 1, UNK), sex (M/F) was used to estimate the HR. Results: A total of 5898 patients were included in this analysis. The median age was 65 years (range 30-91 years). A total of 87(1.5%) patients were underweight, 1853 (31%) were normal weight, 2212 (38%) were overweight, 1332 (23%) were obese, and 414 (7%) had missing BMI. The results of the multivariate analysis of PFS and OS are shown in the Table. Conclusions: Exploratory analysis of patients with RRMM found that patients who were overweight and obese had a trend towards slightly improved PFS and OS when compared to normal weight patients. Similar trends were observed in the analyses of overall response rate and BMI (not presented in the abstract). These results are consistent with previous studies in other malignancies. Limitations include the lack of adjustment for multiple testing, the small sample of patients in the underweight category, and heterogeneity in the treatment regimens and PFS assessments in the clinical trials included in the analysis. Future studies are needed to evaluate safety and impact of treatment regimens on efficacy outcome measures based on body weight.