We have designed, synthesized, and characterized a short (32-mer; 8-nm), single-stranded, collagen-related peptide (CRP), 1a, which forms triple-helical building blocks that self-assemble into large, composite fibrils by strictly noncovalent means. Computational analysis suggested that the installation of complementary, aromatic pi-stacking recognition elements at the N- and C-termini of (Gly-Pro-Hyp)(10) would facilitate the head-to-tail assembly of triple-helical subunits. Our CD, H-1 NMR, DLS, and TEM results for 1a support the formation of such triple-helical, supramolecular structures. Consistent with self-assembly into micrometer-size, composite fibrils, 1a induced the aggregation of human platelets with nearly the same potency as native Type I collagen. The aromatic-aromatic recognition motif employed in this study provides a straightforward approach to collagen-mimetics and has important implications for the design of triple-helical building blocks that can spontaneously oligomerize into functional fibrillar structures.