In basic probability courses, addressing the issue of random vectors shows that the marginal distributions of such vectors can be obtained in a unique way from the joint distribution. The reciprocal of this affirmation does not necessarily have. This article of informative type, tries, by means of a counterexample taken from Embrechts et al. (2002), and that makes use of the theory of copulas, to illustrate the fallacy: “ Marginal distributions and correlation determine the joint distribution ”.Keywords: correlation coefficient; joint distribution; marginal distribution; bivariate normal distribution; copulation theory; random vectors.