In patients with rheumatoid arthritis (RA), weight is an important prognostic factor. Preliminary evidence has indicated that treatment with anti-tumour necrosis factor (TNF) therapy can affect the weight of patients with RA, but the relationship between improved prognosis and weight changes remains to be clarified. Our aim was to investigate the effects of anti-TNF therapy on the weight of patients with RA following 24 months of treatment. Patients (n = 168) were selected for this retrospective analysis on the basis of having received anti-TNF therapy for the first time. Change in body weight after 12 and 24 months of treatment was calculated and analysed by multiple regression analysis using age, sex, baseline body mass index (BMI), baseline DAS28 score, disease-modifying antirheumatic drug use, steroid use and specific anti-TNF drug as explanatory variables. The mean weight change of the patient group after 12 months of treatment was +1.58 kg (95% CI 0.71 to 2.46 kg) and after 24 months was +1.80 kg (95% CI 0.69 to 2.67 kg). After 24 months, 64.3% of patients had gained weight. There was no statistically significant association between weight gain at 12 or 24 months and age, sex, steroid use at baseline, anti-TNF drug or baseline DAS28 score. Baseline BMI had a statistically significant negative association with weight gain at 12 and 24 months. RA patients with lower BMIs tend to gain weight with anti-TNF therapy. Further studies are required to determine if the weight gained is fat and/or muscle and the effects upon general health outcomes.