Significance The translational GTPase LepA is a highly conserved bacterial protein whose role in the cell has been elusive. Here, we show that the function of LepA lies in biogenesis of the 30S subunit of the ribosome, rather than in translation elongation, as previously supposed. Loss of LepA results in the accumulation of immature 30S particles lacking certain proteins of the 3′ (head) domain and containing precursor 17S rRNA. The GTPase activity of LepA, like that of other translational GTPases, is stimulated by interactions with both subunits of the ribosome. This implies that LepA acts at a late stage of assembly, in the context of the 70S ribosome.