In this study, a method for assessing the occurrence of trace amounts of 12 representative estrogenic compounds in sewage and surface waters was developed. The selected substances were the phytoestrogens daidzein, genistein and biochanin A, the alkylphenols bisphenol A and 4-nonylphenol, the natural hormones 17β-estradiol, estrone, estriol and the synthetic hormone 17α-ethynylestradiol and the mycoestrogens zearalenone and two of its metabolites (α-zearalanol and β-zearalanol). The procedure consists in solid phase extraction (SPE) performed with OASIS cartridges followed by liquid chromatography coupled with tandem mass spectrometry (LC–MS–MS). Recoveries were all above 80% for each analyzed aqueous matrices. The developed method was applied to verify the occurrence of endocrine disrupters in environmental samples of sewage influents and effluents of an Italian STP. Phytoestrogens were present in effluents at concentrations ranging from 3 to 83 ng/l, whereas the levels detected for alkylphenols were in the range 13–36 ng/l for bisphenol A and up to 1 μg/l for nonylphenol. Estrogens and zeranols were determined at levels below 30 ng/l. Analysis of a river (Tiber) receiving effluent waters revealed high quantities of bisphenol A (15–29 ng/l) and nonylphenol (up to 1.2 μg/l), whereas the presence of all the other compounds were at levels of few ng/l.