OBJECTIVE To evaluate the long-term safety and efficacy of varicella vaccination in children with juvenile idiopathic arthritis (JIA) treated with biologics. METHODS We performed a prospective study with long term follow up. Six patients with JIA treated with biologics, received 2 doses of varicella vaccine. Before vaccination, JIA was stable on therapy and peripheral blood lymphocyte populations were within normal limits. After vaccination, children were followed for disease activity, infections and production of protective antibodies. RESULTS There were no serious side effects after vaccination and no varicella infection. Disease activity remained stable. Five patients (83%) produced protective antibodies against varicella virus 6 weeks after the second vaccination. One patient with low level of protective antibodies got mild varicella infection 4 months after the second vaccination. CONCLUSION Varicella vaccination appears to be safe in our group of six JIA patients treated with biologics. Vaccination does not always protect against varicella infection.