Comparability of monitoring data are essential for any meaningful assessment and for the management of environmental risks of emerging pollutants. The reliability and comparability of data at European level is often limited, because analytical methods for emerging pollutants are often not fully validated, not harmonized or not suitable for all relevant matrices. This paper describes a collaborative interlaboratory exercise for the analysis of non-steroidal anti-inflammatory drugs (NSAIDs) residues in freshwater and wastewater, held in the framework of the EU project "Network of reference laboratories for monitoring of emerging environmental pollutants" (NORMAN). The NSAID compounds selected in this study were ketoprofen, naproxen, ibuprofen and diclofenac. Thirteen laboratories distributed along nine European Countries (Austria, France, Germany, Greece, Italy, Slovak Republic, Slovenia, Spain, and Switzerland) took part in this exercise, 126 samples were analyzed and a total number of 473 values in duplicate were collected. Samples selected in this study include environmental water (river water and waste water) and artificial water (fortified environmental and distilled water) with different ranges of complexity. Two analytical methods were proposed by the organiser; one is based on the use of solid phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and the second one is based on SPE followed by gas-chromatography-mass spectrometry (GC-MS), however, in the first round some different approaches were also admitted. The main goals of this interlaboratory comparison were to evaluate the available analytical schemes for NSAID analysis in natural waters, to evaluate the repeatability (r) and reproducibility (R) between participating laboratories, and to evaluate the influence of the analytical method and sample matrices on the results.