Fusobacterium nucleatum is one of the most frequently cultured bacteria from subgingival plaque. It can be isolated from active periodontal lesions as well as from healthy sites. Currently, F. nucleatum has been divided into five subspecies. An early hypothesis suggested an association between certain subspecies and periodontal disease or health. On the other hand, a broad heterogeneity between F. nucleatum isolates has been suggested, so that the subspeciation scheme and therefore the proposed association may not be valid. The purpose of the present study was to analyze if clonal differences exist between human F. nucleatum isolates from either periodontally healthy or diseased individuals. 23 F. nucleatum isolates from periodontally healthy and 17 isolates from periodontally diseased individuals were analysed by ribotyping. A broad genetic heterogeneity was present, although some of the isolates from periodontally healthy individuals were genotypically identical. However, no clonal differences between isolates from periodontally healthy or diseased individuals was detected.