Three stromal corneal dystrophies (granular, lattice type l, and Avellino) were recently mapped to a single locus on chromosome 5. This study was conducted to determine if there is histologic evidence to support the allelic relationship suggested by the genetic studies. We examined 23 corneal buttons from the two families with lattice dystrophy and 13 corneal buttons from the two families with granular dystrophy who were involved in the chromosomal linkage studies. In the two families with clinically typical granular dystrophy, one corneal button also contained focal amyloid deposits. In both families with clinically typical lattice dystrophy type 1, we found evidence of granular deposits. The genetic linkage studies demonstrate only that the disease-causing mutations for these three stromal dystrophies share the same genetic locus. However, the evidence of histologic overlap strongly suggests that these dystrophies are caused by mutations within the same gene.