We have probed the nature of the individual kinetic steps in the folding of the Tetrahymena ribozyme by studying the folding kinetics of mutant ribozymes. After rapid formation of the first structural subdomain, a slow step precedes stable formation of the second subdomain. The two central helices of the second subdomain form in an interdependent manner, and this structural subunit therefore also constitutes a kinetic folding unit. The slow folding step includes formation of tertiary interactions in a triple-helical scaffold that orients the two subdomains of the RNA. The rapid and early formation of short range secondary structure, the hierarchical formation of kinetic folding units corresponding to structural subdomains, and the formation of tertiary interactions between subdomains late during the folding process appear to be common features of the folding mechanism for both RNA and proteins.