Primary drug resistance is an emerging problem in HIV infections. We have investigated the current prevalence of primary resistance in Korea and compared it with previous data. Drug-naive HIV patients attending the outpatient clinic of Seoul National University Hospital between April and August 2006 were enrolled. A medical interview and a genotypic resistance test were performed for each patient. The International AIDS Society-USA Panel consensus statement issued in 2006 was used to define resistance mutations. Eighty-one drug-naive HIV patients were enrolled. Two (2.5%) were infected with primary drug-resistant virus: M41L and K103N, respectively. In our previous study, conducted between 1998 and 2002, three (6%) of 50 subjects harbored resistant viruses. Thus the frequency of primary resistance was lower in the present sample than in the earlier one, though the difference is not statistically significant (p = 0.37). In view of our findings, routine antiretroviral resistance tests for drug-naive HIV patients are not obligatory in Korea.