Paediatric varicocele is a well known entity but its effect on adult infertility has not been adequately clarified. Since measurement of testicular volume is currently the best method of estimating the male reproductive potential, 945 boys aged between 13 and 18 years were examined with regard to testicular volume and the incidence of varicocele. The average volumes for right and left testes were 15.087 +/- 0.237 and 14.514 +/- 0.347 ml respectively, and the incidence of varicocele was 16.7%. The incidence increased from 14.5 to 21.7% as the ages increased from 14 to 18. The differences in volume of the 2 testes in boys with varicocele were statistically significant when compared with the normal group, but this significance failed to become more pronounced when the slight varicocele group (grade I) was included with the normal group and compared with the severe varicocele group (grades II and III). There may be no significant differences between the volumes of the 2 testes in boys with varicocele when careful measurement and strict statistical analyses are applied. However, some boys in the varicocele group were found to have testicular volumes below the confidence interval (mean - SE) or under 1 SD, and the 2 testicular volumes differed in certain age groups. This group requires further follow-up. The results of this study have added further contradictory findings to the issue of paediatric varicocele in terms of testicular atrophy, estimation of potential fertility and the indications for immediate surgery. There is a need for further prospective controlled trials.