This work describes the development of a two-phase hollow fiber liquid phase microextraction method for the determination of three hydrophobic transformation products of the nonsteroidal anti-inflammatory drugs ketoprofen, ibuprofen and diclofenac: 3-acetobenzophenone, 4´-isobutylacetophenone and diclofenac amide. The optimized method involved extraction for 180min at a stirring speed of 440rpm. Hollow fibers (0.6mm i.d.) of 6cm length were employed and the acceptor phase consisted of 1-octanol. 5% Sodium chloride was added to samples to prevent loss of the solvent during extraction. Extracts were analyzed by GC-MS and method detection limits were in the range of 1.6-5.6ngL(-1). The method was applied for the determination of target analytes in influent samples from five Swedish wastewater treatment plants (WWTPs). All three analytes were found in very low or non-detectable concentrations. The most abundant compound was 3-acetobenzophenone found at four of the investigated WWTPs at an average concentration of 62ngL(-1). Diclofenac amide and 4'-isobutylacetophenone were only detected above LOD at one WWTP each at a concentration of 55 and 197ngL(-1), respectively. Samples of water entering and exiting the activated sludge treatment as well as digested sludge were also collected from one of the WWTPs. Only diclofenac amide was detected in these samples. A higher concentration was detected in the effluent from the activated sludge treatment than the influent, thus indicating the formation of this compound during treatment. In the sludge, diclofenac amide was detected at 183ngg(-1)wet weight. Based on these results it can be concluded that the amounts of these compounds reaching WWTPs are very small, suggesting negligible risks to the aquatic environment. However, they also indicate the potential formation during the activated sludge process and accumulation into sludge for at least one of the compounds which is why further studies of these processes are needed.