Powder X-ray diffraction data of melatonin C13H16N2O2 were collected on a conventional X-ray powder diffractometer: the monoclinic cell parameter are a=7.7416(8) Å, b=9.2897(9) Å, c=17.1444(16) Å, β=96.756(9)°, volume 1224.4(3) Å3 (space group P21/c). The strongest lines are (d (Å), I/I0) 8.161 (100), 5.411 Å (46), 3.412 Å (34), 4.668 Å (33), 4.645 Å (25), 3.554 Å (22), 3.668 Å (16), and 4.483 Å (14). Reported intensities are validated by Rietveld analysis. The data consist of measured positions and intensities and cover an angular range up to 60° 2θ: experimental, calculated, and difference patterns are also reported.