Some evidences suggest that obesity impairs the effectiveness of TNF inhibitors. We examined the impact of body mass index (BMI) on the clinical effectiveness of abatacept in rheumatoid arthritis (RA) patients. This is a pooled analysis of 10 prospective cohorts of RA patients. All patients with available BMI were included in this study. The primary endpoint was drug retention of abatacept in the different BMI categories. Multivariable Cox regression was used to estimate hazard ratios (HRs) for drug discontinuation. A secondary endpoint was EULAR/LUNDEX response rates at 6/12 months. Of the 2015 RA patients initiating therapy with IV abatacept, 380 (18.9%) were classified as obese. Obese patients had more functional disability, and were less often RF positive. The median abatacept retention time was 1.91 years for obese RA patients compared to 2.12 years for non-obese patients (p = 0.15). The risk of abatacept discontinuation was not significantly different for overweight (HR 1.03 (95% CI 0.89-1.19)), or for obese (HR 1.08 (95% CI 0.89-1.30)) compared to normal-weight patients. Rheumatoid factor positivity reduced the risk of abatacept discontinuation (HR 0.83 (95% CI 0.72-0.95)), while previous biologic therapy was positively associated with drug interruption (HRs increasing from 1.68 to 2.16 with the line of treatments). Obese and non-obese patients attained similar rates of EULAR/LUNDEX clinical response at 6/12 months. Drug retention and clinical response rates to abatacept do not seem to be decreased by obesity in RA patients.