The evolutionarily conserved proteins REI1-LIKE (REIL1) and REIL2 have four conserved zinc finger domains and are Arabidopsis thaliana homologs of the cytosolic 60S ribosomal maturation factor Rei1p (for Required for isotropic bud growth1 protein) from yeast (Saccharomyces cerevisiae) and its paralog Reh1p (for REI1 homologue1 protein). The yeast and A. thaliana paralogs result from independent gene duplications. The A. thaliana REIL paralogs are required specifically in the cold (10°C) but not for growth at optimal temperature (20°C). A reil1-1 reil2-1 double mutant is arrested at 10°C prior to the emergence of the first rosette leaf. Two allelic reil2 mutants, reil2-1 and reil2-2, form small spoon-shaped leaves at 10°C. This phenomenon reverts after emergence of the inflorescence in the cold or upon shift to 20°C. Except for a slightly delayed germination, a reil1-1 mutant shows no further growth phenotype under the currently investigated conditions. A comparative analysis demonstrates conserved coexpression of orthologous genes from yeast and A. thaliana that are coregulated with yeast rei1 or with A. thaliana REIL2, respectively. The conserved correlations point to a role of A. thaliana REIL proteins in the maturation of the eukaryotic ribosomal 60S subunit. We support this conclusion by heterologous complementation of the cold-induced growth defect of the yeast Δrei1 deletion.