One hundred sixty consecutive patients with the Marfan syndrome were reviewed for ocular, cardiovascular, and skeletal abnormalities, and were graded by severity. The most striking ocular abnormality was enlargement of the globe, presumably caused by scleral stretching. Staphylomata were not a feature of any of the patients seen, nor was keratoconus. The cornea, in fact, was flattened but not thinned. Among the 160 patients, 193 eyes showed dislocation of the lens. Dislocation of the lens was positively correlated with increased ocular axial length and with decreasing KJ readings. We postulate that the ocular pathologic changes are primarily caused by stretching of the tunica scleralis, and that the zonular fibers (thus under stress may "give" or may rupture in their area of presumably least density which may be the area of developmental fusion of the optic vesicle. In a small proportion of cases the lens dislocation was progressive. There was no correlation between ocular findings, on one hand, and the skeletal and cardiovascular abnormalities on the other. However, there was a good degree of intrafamilial consistency with regard to absence or presence of ocular pathology. The absence of correlation between the ocular and systemic findings in our data on these 160 patients is best explained by the existence of more than 1 point mutation, which may give rise to different but clinically similar phenotypes. The results of our calculations of mutation rate were compatible with such an explanation.