THE TITLE COMPOUND [SYSTEMATIC NAME: fluoren-9-yl N-(1-carb-oxy-3-methyl-butyl)carbamate], C(21)H(23)NO(4), exhibits torsion angles that vary from the typical values found in other Fmoc-protected amino acids, viz. the orientations of the fluorene and carboxyl groups [C-O-C-C = 93.8 (2) and N-C-C=O = -23.6 (2)°]. The crystal structure exhibits two inter-molecular hydrogen bonds (O-H⋯O and N-H⋯O) that link the mol-ecules into two-dimensional sheets parallel to the ab plane.