Collagen molecules in native 66.8 nm (D) periodic fibrils are widely believed to be assembled into discrete, rope-like sub-structures, or microfibrils1-17. Several types of microfibril have been proposed (2,4,5,7- and 8-stranded), mainly on the basis of information contained in the medium angle X-ray diffraction patterns of native tendon fibres1,5-7. These patterns show a series of equatorial and near-equatorial Bragg reflections which indicate that the collagen molecules are arranged on a three-dimensional crystalline lattice. The 4-stranded11, 5-stranded4-6 and 8-stranded7,8 microfibrils are D-periodic with approximate diameter 3.8 nm, and these and the 2-stranded10 model are supposed to be packed on a three-dimensional lattice whose basal unit cell, (approximately) perpendicular to the fibril axis, is tetragonal (or quasi-tetragonal) with side a, √2 symbol or 2a, where a is ~ 3.8 nm. In this paper we describe a re-interpretation of the X-ray data5,6 which leads to a new model for the crystalline regions of the fibril, based on quasi-hexagonal molecular packing without microfibrillar sub-structures, and hence having the character of a molecular crystal18.