The spatial distribution of the terminal groups of poly(amido amine) dendrimers have been determined experimentally by small-angle neutron scattering with deuterium labeling and scattering contrast variation. The radius of gyration of deuterated terminal units of generation 7 dendrimers is 39.3 +/- 1.0 Angstrom. This is significantly larger than the radius of gyration of the whole dendrimer, which is 34.4 +/- 0.2 Angstrom. These data indicate that dendrimers have terminal groups that; are concentrated near the periphery. These results are inconsistent with many computer simulations and some molecular models.