Over the past 10 years there has been a pronounced increase in the number of cases of genital herpes seen in sexually transmitted disease (STD) clinics in the United Kingdom. The reporting system, however, does not differentiate between primary and recurrent infections, and consequently any increase in the number of patients reattending clinics with recurrent genital herpes would falsely inflate the statistics. A study of cases of herpes seen in the department of genitourinary medicine of this hospital in the two years 1972 and 1982 is presented. It showed that the proportion of patients attending with recurrent herpes had increased from 18% in 1972 to 31% in 1982. As a result of this, the 68% increase between 1972 and 1982 in the total number of cases of herpes seen in the clinic overestimates the real increase in the size of the problem, which is closer to 40%, based upon cases of primary herpes only. Modifications to the national recording system are necessary to overcome the problems highlighted by this study. These modifications could include classifying each case of genital herpes as primary, recurrent, or recurrent but not previously recorded, which would provide a more accurate picture of the size of the problem of genital herpes in the population.