The objectives of this study were to compare the patient's (PtGDA) and physician's (PhGDA) assessment of global disease activity and to identify factors that might influence these differences as well as factors that may influence the patient's and the physician's scores separately. Anonymous data were used from 2,117 Dutch patients included in the Measurement of efficacy of Treatment in the Era of Rheumatology database. PtGDA and PhGDA were scored independently on a 100-mm visual analog scale (VAS) with 0 and 100 as extremes. The agreement, intraclass correlation coefficients (ICC), was calculated and a Bland-Altman plot was created to visualize the differences between PtGDA and PhGDA. Linear mixed model analysis was used to model PtGDA and PhGDA. Logistic repeated measurements were used to model the difference in PtGDA and PhGDA (PtGDA > PhGDA versus PtGDA ≤ PhGDA). Gender patient, gender physician, age, swollen joint count (SJC), tender joint count, VAS pain, disease duration, and erythrocyte sedimentation rate (ESR) were considered as possible determinants in both models. Mean (standard deviation) age was 57 (15) years and 67% of the patients were female. Agreement between PtGDA and PhGDA was moderate (ICC, 0.57). Patients scored on average 11 units higher (worse) than rheumatologists (95% limits of agreement, -25.2 to 47.6). Patient's perception of pain (VAS) was positively associated with a PtGDA being higher than PhGDA. Similarly, ESR and swollen joint counts were positively associated with a PtGDA being lower or equal to the PhGDA. Patients rate global disease activity consistently higher than their rheumatologists. Patients base their judgment primarily on the level of pain, physicians on the level of SJC and ESR.