We sequenced and phylogenetically analyzed the reverse transcriptase (RT) region of five human immunodeficiency virus type 1 isolates from treatment-naive Ethiopian émigrés to Israel. Heteroduplex mobility assays were performed to confirm the clade C status of env genomic regions. The RT sequences showed that the strains clustered phylogenetically with clade C viruses, and a KVEQ-specific motif of silent mutations (amino acids 65, 106, 138, and 161, respectively) at resistance sites was present in the polymerase region of all studied Ethiopian isolates and subtype C reference strains. In addition, many other silent mutations were observed in the clade C viruses at various resistance sites. In general, the Ethiopian isolates were more closely related genotypically to a clade C reference strain from Botswana (southern Africa) than to previously sequenced Ethiopian reference strains. Genotypic analysis showed that two Ethiopian isolates naturally harbored the mutations K70R and G190A associated with resistance to ZDV and nonnucleoside reverse transcriptase inhibitors, respectively. Phenotypic assays revealed that the K70R substitution in this context did not reduce susceptibility to ZDV, whereas the G190A substitution resulted in high-level resistance to nevirapine (NVP). Moreover, variants resistant to NVP, delavirdine (DLV), and efavirenz (EFV) were more rapidly selected at lower drug doses culture with clade C than with clade B wild-type isolates. In the case of subtype C, selection with NVP and/or EFV led to the appearance of several previously unseen mutations in RT, i.e., V106M and S98I, as well as other mutations that have been previously reported (e.g., K103N, V106A, V108I, and Y181C). After selection with DLV, a polymorphism, A62A, initially observed in the Ethiopian isolate 4762, mutated to A62V; the latter is a secondary substitution associated with multidrug resistance against nucleoside RT inhibitors. Phenotypic analysis of clade C mutants selected against NVP, DLV, and EFV revealed broad cross-resistance, particularly in regard to NVP and DLV. These findings suggest that RT genotypic diversity may influence the emergence of drug resistance.