Gardner Syndrome (GS) is an autosomal dominant variant of colorectal polyposis with essentially complete penetrance. It is distinguished from the other polyposis syndromes by its delayed age at onset, the number of polyps, and its extracolonic manifestations. The presence of epidermal cysts, bony osteomata, desmoid tumors, and dental anomalies are distinguishing features of this syndrome. Recently, multiple and bilateral patches of congenital hypertrophy of the retinal pigment epithelium (CHRPE) have been described in three families with classical GS. Tight linkage of the GS and CHRPE phenotypes (Z = 9.752; theta = 0) suggested that CHRPE is a pleiotropic effect of the Gardner mutation within the families in which the ophthalmic trait occurs and is thus a useful marker for the early detection of GS gene carriers. We have analyzed six new families segregating for classic GS and CHRPE. Linkage was tested between GS and CHRPE and between these two phenotypes and a battery of 22 informative biochemical and serological markers. We have extended the linkage analysis on two GS-CHRPE families originally reported elsewhere. Linkage between GS and CHRPE at theta = 0 was observed in all families, a result supporting our original suggestion that CHRPE is a congenital manifestation of the GS mutation. Exclusionary linkage data presented confirm that, for linkage analysis in these families, the CHRPE phenotype is a more powerful marker than other phenotypic features of GS.