A frequency-modulated Nd:YLF laser has been mode locked at a repetition rate of 5.4 GHz by using 20 mW of microwave power applied to a LiTaO3 electro-optic phase modulator in a short (2-cm) laser cavity. The 13-ps pulse duration is shorter than expected on the basis of mode-locking theory for homogeneously broadened transitions and is attributed to inhomogeneity associated with spatial hole burning.