An X‐ray diffraction study was carried out on a single crystal of N‐(Nα‐[(tert.‐butyloxy)‐carbonyl)‐l‐alanyl)‐N,Nα‐dicyclohexylurea belonging to the tetragonal space group P41212, having cell dimensions a = b= 10.102(3) Å, c = 46.067(7) Å, V = 4701.2 Å3, Z = 8. The crystal structure was solved by direct methods and refined to an R value of 0.056 for 1602 unique reflections with I<2.5 σ(I). Crystal structure analysis shows the presence of an intramolecular N–H O=C H‐bond stabilizing the molecule in a folded form similar to that of a β turn, forming a nine‐membered ring. IR and 1H‐NMR studies in CDCI3 solution confirm the stable folded conformation found in the crystalline state, as well as the existence of N–H O=C H‐bonds in the title compound, as in peptides. Copyright © 1992, Wiley Blackwell. All rights reserved