Since the 1988 World Health Assembly resolution to eradicate poliomyelitis, three World Health Organization (WHO) regions (Americas, Western Pacific, and European) have been certified polio-free, and the number of countries where polio is endemic has decreased from 125 in 1988 to six in 2003 (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan). In 2003, Nigeria, the most populous country of the African continent (2003 population projected from 1991 census report: 125 million), reported 355 wild poliovirus (WPV) cases, accounting for 45% of cases reported globally and >80% of cases reported from the African Region (AFR). This report summarizes progress toward polio eradication in Nigeria during January 2003-March 2004. The findings indicate the urgent need to implement high-quality supplementary immunization activities (SIAs) in Nigeria to interrupt ongoing WPV transmission.