High production rates and wide areas of application of water-soluble polymers indicate their potential occurrence in wastewater. Poly(N-vinylcaprolactam) (PNVCL) is such a water-soluble and poorly biodegradable polymer with non-ionic, non-sticky, non-toxic and thermosensitive properties. Its field of applications covers being a constituent in aerosol sprays, pump sprays, and lotions as well as its usage as flocculant in wastewater treatment plants. However, although discharged into sewage treatment plants at high amounts, analytical methods for determining water soluble polymers, in particular PNVCL, in environmental samples are still missing. Therefore, this study aims at developing an efficient analytical method for detecting trace levels of poly(N-vinylcaprolactam) in wastewaters by applying continuous-flow off-line Py-GC/MS for the first time. The approach was based on the identification of specific off-line pyrolysis products (ε-caprolactam, N-vinylcaprolactam) that haven been used in the following for a calibration process that allowed a quantitative determination. An evaluation including specificity, linearity, sensitivity and reproducibility characterized this approach as very suitable for detection of this polymer in complex environmental matrices such as wastewaters. Finally, the transferability has been checked by analyzing a real wastewater from a sewage treatment plant effluent. Here limitations especially due to matrix effects are lowering the sensitivity of the pyrolysis-based method. Nevertheless, a contamination with approx. 70 µg/L of poly(N-vinylcaprolactam) was determined pointing to a huge emission of PNVCL into the aquatic environment and a general high environmental relevance of this synthetic polymer. Noteworthy, this is the first report on the occurrence of poly(N-vinylcaprolactam) in environmental samples.