A multiresidue method for the quantification of 13 sulfonamides in animal feed is described. It involves the application of a modified QuEChERS procedure followed by HPLC–MS/MS (high performance liquid chromatography coupled to tandem mass spectrometry) analysis. The best conditions for the extraction solution and PSA (primary secondary amine) mass were determined. After optimization, the method was validated according to the European Commission Decision 2002/657/EC. The validation levels employed were 25, 50 and 75 μg kg−1. Acceptable values were obtained for the following parameters: linearity (0.9864 < r2 < 0.9993), decision limit (50.4 μg kg−1 < CCα < 55.8 μg kg−1), detection capability (50.7 μg kg−1<CCβ < 55.8 μg kg−1), limit of quantification (0.9 μg kg−1 < LOQ < 7.1 μg kg−1), accuracy (86.0 < recovery rates < 106.8), precision (3.6 < repeatability < 19.5), (5.5 < intermediate precision < 21.6), measurement uncertainty (MU) (4.1 < MU < 32.6) and selectivity. These findings met the Codex requirements, which allow for the routine use of the method by the laboratories linked to the Ministry of Agriculture, Livestock and Food Supply of Brazil. Finally, the method was applied to real samples and only one of them showed positive for sulfamethazine, however, with a concentration below the LOQ of the method.