Water deficit and rain irregularity are key factors limiting agricultural production in the Mediterranean basin. This study aims at assessing the effect of water deficit on the vegetative development and forage yield (leaves plus stems) in some populations of Medicago aculeata, Medicago orbicularis and Medicago truncatula. For this reason, plants were subjected to two water regimes during the vegetative phase: one satisfying the plant's water requirements and the other being water deficient. At the end of the vegetative phase, plants were uprooted and the following parameters were evaluated: length of the branch carrying the first flower, number of primary branches, number of inter-nodes and forage yield (leaves plus stems). The results obtained showed that water deficit considerably reduced the different plant's organs and reduced forage yield (leaves plus stems) in the three Medicago L. species.