Careful high-resolution X-ray diffraction measurements at 105 K have been used to map the electron deformation density of the free base form of norcocaine, a major metabolite of cocaine. Intensities of 18 890 reflections were measured from three crystals with Mo K alpha radiation to a resolution of (sin theta/lambda)(max) = 1.07 Angstrom(-1). Averaging symmetry-related reflections yielded 8247 unique reflections. A least-squares refinement procedure has been used in which multipole parameters are added to describe the distortions of the atomic electron distributions from spherical symmetry. The refinement also includes improved estimates of the X-ray structure factor phases, which have been used to plot maps of the electron density distribution. Molecular electrostatic potentials have been calculated from the electron densities determined in the least-squares multipole refinement. A region of negative electrostatic potential around the carbonyl oxygen atom in the methoxycarbonyl group clearly defines the oxygen atom as reactive toward electrophilic attack. In addition, a deep negative potential around the basic, bridging nitrogen atom exists. Both of these atoms are involved in an intramolecular hydrogen bond. Net atomic charges calculated from refined monopole population parameters yielded charges of -0.25(5) for the methoxycarbonyl and 0.03(5) for the benzoyl functional groups. The tropane ring system had a net charge of +0.23(5).