Objective. To assess the validity, reliability, and feasibility of the Systemic Lupus Activity Measure-Revised (SLAM-R), the Mexican version of the Systemic Lupus Erythematosus Disease Activity Index (MEX-SLEDAI), and a Modified SLEDAI-2000 (SLEDAI-2K) compared with the SLEDAI-2K in a multiethnic population of patients with SLE. Methods. We studied 92 SLE patients from 3 US geographic areas (Alabama, Texas, and Puerto Rico). Assessment occurred during regular outpatient, inpatient, or study encounters. A trained physician scored the 4 instruments and also assessed disease activity globally [physician global assessment (PGA)]. Convergent (with SLEDAI-2K) and construct validity (with PGA) were determined by Spearman rank (rs) correlation test. Level of agreement between the instruments was assessed using Bland-Altman plots. Discriminant validity (distinguishing clearly active vs mildly/nonactive disease) was assessed considering the SLEDAI-2K (and the PGA) as the gold standard. Feasibility was explored by cost analyses. Results. The SLAM-R, the MEX-SLEDAI, and the Modified SLEDAI-2K were highly correlated with the SLEDAI-2K (rs = 0.566, 0.755, 0.924, respectively) and with the PGA (r s = 0.650, 0.540, 0.634, respectively). The 3 instruments showed good agreement with the SLEDAI-2K (Bland-Altman plots). The Modified SLEDAI-2K had better discriminant validity than the SLAM-R and the MEX-SLEDAI. The Modified SLEDAI-2K was the least expensive instrument. Conclusion. The SLAM-R, the MEX-SLEDAI, and the Modified SLEDAI-2K are adequate options for assessment of SLE disease activity; they are also less costly than the SLEDAI-2K.