An explanation is given for the nearly linear relationship between the deuteron radius and the triplet scattering length as predicted by potential models of the {ital NN} interaction. This is accomplished by showing that the quantity {l angle}{ital r}{sup 2}{r angle}/{ital a}{sub {ital t}}{sup 2} can be expanded to high accuracy in terms of the small parameter {ital x}={ital r}{sub {ital t}}/{ital a}{sub {ital t}}. We show that shape dependence only enters at order {ital x}{sup 3} and higher. Possible reasons for the disagreement with the experimental result are discussed.