Determination of the patterns of genomic variation among RNA virus isolates is a powerful approach for establishing their epidemiologic interrelationships. The standard technique for such studies, ribonuclease T1 oligonucleotide fingerprinting, can detect similarities only among very closely related isolates. The rapid evolution of the poliovirus genome during transmission in humans requires the application of alternate methods to identify more distant relationships. To obtain a substantially broader view of the distribution of wild poliovirus type 1 genotypes in nature, we compared 150 bases of genomic sequence information (encoding parts of the capsid protein VP1 and the noncapsid protein 2A) from 62 isolates obtained from poliomyelitis patients in five continents. The partial sequence information allowed us to (1) identify numerous geographic foci of endemic circulation of wild type 1 polioviruses, (2) reveal previously unsuspected links between cases in distant communities, (3) monitor the displacement from the environment of preexisting polioviruses by viruses from other regions, and (4) recognize the recombinant (vaccine-wild; wild-wild) origins of some epidemic polioviruses.