We have synthesized and characterized a series of copolymers of diaminomethane and alpha,omega-dicarboxylic acids (nylons 1,n with n = 5,6,7,8,10, and 12). Their structure has been determined by various methods, including X-ray diffraction and electron microscopy. A new conformation, different from conventional polyamides, has been found. It shows a characteristic shortening of the molecular repeat distance. When n is even, the polymers crystallize in a monoclinic system, space group B2/b11, whereas when n is odd, they crystallize in an hexagonal lattice, space group P3(2)12. A characteristic gauche conformation of the monomethylene bisamide units is in full agreement with all experimental results. The two amide groups in each unit are oriented in opposite directions. Structural differences in the series are explained in terms of conformational changes of the dicarboxylic unit depending on the number of methylene groups.