Comparative analyses of genetic diversity and phylogenetic relationships of sweetpotato (Ipomoea batatas (L.) Lam.) and its wild relatives in Ipomoea series Batatas were conducted using amplified fragment length polymorphism (AFLP) and sequence data from the internal transcribed spacer (ITS) region of the ribosomal DNA. Low ITS divergence among thirteen species of ser. Batatas resulted in poorly resolved relationships. More variable AFLP characters were found to be more efficient in characterizing genetic diversity and phylogenetic relationships at both intra- and interspecific levels within ser. Batatas. Highly informative AFLP fingerprints of 36 accessions representing 10 species of ser. Batatas were generated using only six primer combinations. Of the species examined, I. trifida was found to be the most closely related to I. batatas, while I. ramosissima and I. umbraticola were the most distantly related to I. batatas. The highly polymorphic AFLP markers are a valuable tool in assessing genetic diversity and phylogenetic relationships of sweetpotato and its wild relatives.