A retrospective study was conducted in a large population presenting with infertility to determine whether sperm quality has changed in Korea in the last 10 years. We reviewed sperm concentration, motility and semen volume in 22,249 men from whom semen was collected in our laboratory between January 1989 and April 1998 and analysed according to WHO (1987) guidelines. Mean age of the men was 32 years (range 21-40). Data were collected in healthy men with infertility. The mean sperm concentration was 60.5 x 10(6)/mL from 1989 to 1998. There was no statistically significant difference for each year (p > 0.05). Semen volume and sperm motility were also unchanged during the same time period. There was no significant association between either age or year of birth and semen quality. Of the total population, 4033 men (19.0%) exhibited azoospermia and 8397 men (40. 1%) had normal semen parameters which satisfied the 1987 WHO criteria. The changes observed in the semen parameters analysed in this large population showed no evidence of deteriorating semen quality in Korea over the last 10 years.