A well-known version of the uncertainty principle on the cyclic group Z N states that for any couple of functions f, g ∈ ℓ 2 (Z N ) \ {0}, the short-time Fourier transform V g f has support of cardinality at least N . This result can be regarded as a time-frequency version of the celebrated Donoho-Stark uncertainty principle on Z N . Unlike the Donoho-Stark principle, however, a complete identification of the extremals is still missing. In this note we provide an answer to this problem by proving that the support of V g f has cardinality N if and only if it is a coset of a subgroup of order N of Z N ×Z N . Also, we completely identify the corresponding extremal functions f, g. Besides translations and modulations, the symmetries of the problem are encoded by certain metaplectic operators associated with elements of SL(2, Z N/a ), where a is a divisor of N . Partial generalizations are given to finite Abelian groups.