2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/129476A tetrahedral curve is a (usually nonreduced) curve in P^3 defined by an unmixed, height two ideal generated by monomials. We characterize when these curves are arithmetically Cohen-Macaulay by associating a graph to each curve and, using results from combinatorial commutative algebra and Alexander duality, relating the structure of the complementary graph to the Cohen-Macaulay property.15 pages; minor revisions to v. 1 to improve clarity; to appear in JPAACommutative AlgebraCombinatorics13D02; 13C14; 14M07; 05C38text