Illicit distribution of various illicit or counterfeit drugs containing sildenafil and tadalafil has increased and caused noticeable problems in Korea. This study has been performed to determine the content range of sildenafil and tadalafil in various fake drugs. Among the illicit or counterfeit drugs seized by Korean authorities, 105 exhibits were used for the quantification. HPLC-UV analysis of methanol extractions was used for separation and quantitation of the two target compounds. The most abundant type of fake drug was counterfeit Viagra tablets. Sildenafil was found in 73 exhibits, and tadalafil was found in seven exhibits. Twenty-five exhibits out of the 105 contained both sildenafil and tadalafil. The contents of sildenafil ranged from 4.3 to 453.2 mg; for tadalafil, the range was 2.2-40.4 mg. The proportion of cases of having more than 100 mg of sildenafil was 50 percent and 78 percent had more than 20 mg of tadalafil. Abstract published by arrangement with John Wiley & Sons.