The purpose of this study was to measure the erect penile length and circumference in Korean males. The subjects (n = 279, mean age 26.8, range 20-38 years) were drawn from five colleges and seven companies in the Seoul metropolitan area. The data were collected using a modified standardised self-measurement technique on the erect penis. Measurement tools (paper tapes) were designed for user convenience and to minimise measurement errors. Respondents were carefully instructed how to use the tapes for measuring their penile size after self-stimulation. The distances between marks on the returned tapes were measured with a steel ruler to the nearest 1 mm. Mean length of the erect penis was 126.6 mm (95% Cl 125 to 128 mm, median 125 mm) and mean circumferences were 112.8 mm (95% Cl 83 to 141 mm, median 113 mm) at the base, 107.5 mm (95% Cl 78-137 mm, median 108 mm) at the shaft just below the shaft-glans junction, and 113.3 mm (95% Cl 77 to 146 mm, median 113 mm) at the glans. Measurement variations with age (20-24, 25-29 and over 30 years) were not statistically significant. These Korean men's penises on average had a more or less cylindrical shape which was narrower in the middle and they were smaller by all parameters than published samples of Caucasian men. Korean men need a wider range of condoms than is currently marketed to them.