OBJECTIVE: To determine the reliability of SLE patients' disease activity measurements. METHODS: This was a cross-sectional study conducted (August 2016-December 2017) at 2 main public Peruvian hospitals, 1 with a comprehensive lupus care program. Patients assessed their disease activity with a visual analog scale (VAS) (0-100 mm) or a numerical rating scale (NRS) (0-4) before and after their physician's (MD's) assessment. Demographic and disease-related characteristics were recorded. Reliability of patients' disease activity before and after MD's assessment was determined using Spearman rank correlation. Factors possibly associated with this variability were examined with Spearman rank correlation and Mann-Whitney U test. RESULTS: Two hundred forty, mostly Mestizo, SLE patients were included; mean (SD) age and disease duration (diagnosis) were 34.9 (12.9) years and 10.1 (7.0) years, respectively. The Mexican version of the Systemic Lupus Erythematosus Disease Activity Index was 1.9 (2.7), and the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index was 1.2 (1.5). The correlations between NRS and VAS before and after the MD's assessment were ρ = 0.839; p < 0.001; and ρ = 0.872; p < 0.001, respectively. Visual analog scale and NRS were higher before than after the MD's assessment (VAS 29.3 [26.5] and 26.5 [24.9], p = 0.052; and NRS (1.5 [1.2] and 1.3 [1.1], p = 0.003); only the comprehensive program explained this variability (p = 0.043). The reliability of VAS and NRS was ρ = 0.917 and ρ = 0.861, p < 0.001, before and after for the comprehensive program and ρ = 0.710 and ρ = 0.785, p < 0.001, for before and after for the regular program. CONCLUSIONS: Both VAS an NRS are highly reliable. Patients scored higher before than after their physicians' assessment but that these differences were smaller for the patients in the comprehensive care program than in the regular one.