Context Haemophilus influenzae type b (Hib) conjugate vaccine is not perceived as a public health priority in Africa because data on Hib disease burden and vaccine effectiveness are scarce. Hib immunization was introduced in Kenyan infants in 2001. Objective to define invasive Hib disease incidence and Hib vaccine program effectiveness. Design, Setting, Patients culture-based surveillance for invasive Hib disease at Kilifi District Hospital from 2000 to 2005 was linked to demographic surveillance of 38,000 children aged District, Kenya. HIV infection and Hib vaccination status were determined for children with Hib disease admitted 2002-2005. Interventions Conjugate Hib vaccine within the routine childhood immunization program at ages 6, 10 and 14 weeks from November 2001 Main outcome measures Incidence of culture-proven Hib invasive disease before and after vaccine introduction and vaccine program effectiveness (1-incidence rate ratio) Results Prior to vaccine introduction the median age of Hib cases was 8 months; case fatality was 23%. Among children aged 66, 47 and 7.6 per 100,000, respectively. For children <2 >years, incidence was 119, 82 and 16, respectively. In 2004-2005 vaccine effectiveness was 88% (95% CI 73-96%) among children 87% (95% CI 66-96%) among children 2002-2005, 29 (55%) were age-ineligible to have received vaccine, 12 (23%) had not been vaccinated despite being eligible, and 12 (23%) had received ≥2 doses of vaccine (2 were HIV-positive). Conclusions In Kenya, introduction of Hib vaccine into the routine childhood immunization program reduced Hib disease incidence among children aged 12% of its baseline level. This impact was not observed until the third year after vaccine introduction.