The introduction of a routine varicella vaccination program for children has achieved a significant reduction in morbidity and mortality due to varicella. However, there is still an incidence of chickenpox in those vaccinated, called "varicella breakthrough" (VB). This has led to the inclusion of a 2nd dose vaccination schedule, at an age which could be too late.This study presents 23 cases of children diagnosed with VB (mean age at diagnosis 4.85 years) who had been vaccinated with one dose of varicella vaccine (mean age of vaccination 2.37 years).The mean time between the vaccine and the disease was 2.48 years, with a median of 2.0 years. VB was diagnosed in 13% of children who had been vaccinated the previous year, and 52% diagnosed in the previous two. Therefore many of these patients had suffered the disease before the recommended time of administration of the second dose of vaccine according to the current vaccine schedules.To avoid these vaccine failures, it would be appropriate to bring the two doses of varicella vaccine closer, or even assess the pattern of two consecutive doses.