OBJECTIVES: To profile the weight change observed in rheumatoid arthritis (RA) patients receiving infliximab, in order to understand the expected change in their dosing requirements over time on treatment. METHODS: A total 3211 RA patients (2436 males [24%], 775 females [76%]) with valid bodyweight and follow-up measurements from the BSRBR were analysed. Weight change was initially modelled by follow-up (FUP) number using ordinary least-squares linear regression adjusted for sex and patient's total number of visits. Standard errors were adjusted for clustering on study ID. RESULTS: The main analysis modelled FUP as a categorical variable. This analysis showed that the change in average bodyweight did not follow a steady slope, but rather was characterized by a rapid, statistically significant increase of about 1kg on the first visit after baseline followed by a slow, uneven and statistically nonsignificant upward trend over subsequent follow-up visits. This modelling technique gave a significantly better fit (p=0.006) over that possible if treating follow-up number as a continuous variable. To test for possible biases attributable to drop-out, the analysis was repeated in several subsets of patients who had all completed the same number of follow-up visits. Despite statistically nonsignificant or statistically borderline estimates in these subsets, the findings were similar to those reported in the main results. CONCLUSION: Translating observed bodyweight into an expected number of vials required at each visit using basic 3mg/kg dosing shows that the observed weight gain in the BSRBR's infliximab patients does not correspond to a statistically significant change in the total number of vials of infliximab required. Although the dosing in real-life clinical practice tends to vary, the results of this analysis demonstrate that the weight gain observed during infliximab treatment of RA patients is unlikely to have an independent, critical impact on the resource implications for these patients as their treatment continues.