The use of liquid chromatography/tandem mass spectrometry (LC/MS/MS) can give several benefits in the urinary detection of anabolic steroids (AS) such as avoiding the derivatization step or the possible direct detection of conjugated AS. However, the presence of endogenous compounds with similar structures can interfere with this detection, thus decreasing the reliability of the method. The circumvention of these interferences by the use of different MS/MS transitions has been studied. For 17α-trenbolone, an unusual odd-electron ion has been selected for detection. Using this approach, the interferences have been reduced drastically. The selection of a more specific precursor ion can also help in the circumvention of interferences. This has been shown for 1-testosterone, 5β-androst-1-ene-17β-ol-3-one and oxandrolone where the selection of the uncommon [M+H+MeOH]+ as the precursor ion increased the selectivity of the method. In addition, an approach to identify the endogenous interferences if they have corticosteroid or steroid structure has been evaluated. Precursor ion spectra can be used to define the molecular properties of the interferences and to predict whether it is an endogenous steroid or corticosteroid. The use of some restrictions for the structure can be helpful in outlining a feasible hypothesis. This data and the product ions from likely suspects can be used to identify AS. Using this approach, several endogenous interferences have been elucidated in this case study. The knowledge about the structures of these interferences has been found useful to circumvent their detection in the screening method for AS. Copyright © 2007 John Wiley & Sons, Ltd.