A five-helix secondary structural model is proposed for eukaryotic cytoplasmic 5S rRNA. All available sequence data are consistent with this model including those from Chlorella 5S rRNA whose sequence is revised by data included here. Various architectural features of eukaryotic 5S rRNA are summarized in terms of this secondary structural model. It is observed that previous failures to identify universal models for 5S rRNA secondary structure stem from significant differences in architecture between eukaryotic cytoplasmic and eubacterial 5S rRNAs. The usual four-helix model for eubacterial 5S rRNA secondary structure nevertheless does share several structural features with the five-helix model presented here for cytoplasmic 5S rRNA. It is thus likely that these two classes of 5S rRNA are the result of evolutionary divergence rather than convergence.