For many years it has been acknowledged that Danish and Norwegian men have one of the highest risks in the world for testicular cancer in sharp contrast to neighbouring Baltic men from Finland, Estonia and Lithuania. As an association between poor semen quality and testicular cancer has been established, it was suggested that men from high-risk testicular cancer areas would be more likely to have poor semen quality. However, previous studies were not able to elucidate this question due to their retrospective nature. In prospectively designed and strictly controlled studies of fertile men, the existence of regional differences in semen quality was confirmed. In addition, studies of men from the general populations were undertaken and a similar regional difference in semen quality was detected. Men from the eastern part of the Nordic-Baltic area had better semen quality than men from the western part. These findings parallel the incidence of testicular cancer in these regions. Approximately 20% of young men from Norway and Denmark had sperm concentrations below the World Health Organization reference level of 20 x 10(6) spermatozoa/mL, and approximately 40% had <40 x 10(6) spermatozoa/mL which, according to recent publications, may be the 'threshold' below which fecundity declines. In Denmark, the situation is of concern and a continued surveillance of semen quality in young men was established in 2001 by a government-supported programme.