In the present study, an HPLC-MS/MS method to confirm, in bovine urine, the most common synthetic corticosteroids illegally used as growth promoters in livestock breeding will be presented. An API III-Plus (PE-Sciex) triple quadrupole mass spectrometer, interfaced by means of an atmospheric pressure chemical ionization source to the HPLC system, was used. Urine samples were treated with a sulfatase-glucuronidase mixture to cleave the drug-conjugates and then extracted on C18 disposable columns. LC separations were performed on a reversed-phase C18 column with ammonium acetate 0.1 M/acetonitrile (60/40, v/v) as mobile phase. Detection was performed in multiple reaction monitoring mode, negative ions, selecting fragmentations characteristic of 10 corticosteroids used more frequently. Good results, in terms of sensitivity and specificity have been obtained for nine corticosteroids that can be analyzed in the same HPLC run; the limits of sensitivity achieved were 0.05-1.0 ng/ml in urine. Only a more polar corticosteroid, required a different HPLC separation. Practical applications of this technique to real samples proved that it is an effective method to confirm the illegal use of corticosteroids as growth promoter in animal. In comparison with the chemical GC-MS methods the simpler sample preparation and the faster time of analysis permit a considerable increase of sample testing per day without compromising on analytical sensitivity and specificity.