This chapter presents the final example, demonstrating the crystal structure determination of a simple organic compound—a well-known active ingredient in pain relievers, commonly referred to as acetaminophen or Tylenol—from powder diffraction data collected on a standard laboratory X-ray powder diffractometer by means of the simulated annealing Monte Carlo method. It also covers ab initio indexing of the unit cell, Le Bail fitting, and restrained Rietveld refinement. This example may be useful to those interested in pharmaceutical structures, particularly since the imperfect crystallinity observed in this specimen is common in such compounds.