OBJECTIVES: The aim of the study was to conduct secondary analyses of trial data to determine whether taking famciclovir within 12 hours of first perceiving the symptoms of genital herpes was related to decreased outbreak severity and improved healing. METHODS: Data were derived from a double-blind, randomised, active-controlled study of patient-initiated therapy comparing a 2-day course of famciclovir with a 5-day course (total dose 1,50 mg in both courses) in adults with genital herpes. Patients completed the Herpes Symptoms Checklist (HSC) on each day of the five day study period. The proportion of patients healed (without lesions) at day 5 was also determined. RESULTS: Data were available for 501 patients (male = 58.5%; mean age (sd) = 39.2 (11.6) yrs). For the combined treatment groups, patients who took their medication within 12 hours had significantly lower HSC scores on day 1 (within 12 hours, median HSC=6; above 12 hours, median HSC=8; Mann-Whitney U=12,733.5, p<0.05). Patients who took their medication within 12 hours also had significantly lower HSC area under the curve scores for the 5 day study period (AUC; within 12 hours, median HSC=3.8; above 12 hours, median HSC=5.1; Mann-Whitney U=12,751.0, p<0.05). These differences were not apparent for the treatment groups separately. There was a significant association between the time at which the patients took their medication and whether or not they were healed at day 5 for the combined sample (Chi-square = 4.95, p<0.05). This finding was also observed for the 2-day treatment group (Chi-square=6.11, p <0.05) but not for the 5-day treatment group (Chi-square=0.49, p=0.48).  CONCLUSIONS: Taking famciclovir within 12 hours of first becoming aware of genital herpes symptoms is associated with decreased symptom severity and speed of healing. The 2-day treatment, when taken within 12 hours, is associated with a higher rate of healing by day 5.