The use of new psychoactive substances (NPS) has become an important worldwide concern. In particular the use of highly potent fentanyl analogues forms a great health threat to users. In this publication, we detail the characterization of a new fentanyl analogue N-(4-hydroxyphenyl)-N-(1-phenethylpiperidin-4-yl)-butyramide (p-hydroxy-butyrylfentanyl) encountered in drug casework in the Netherlands. Characterization was performed using ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF-MS), gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray fluorescence (XRF).