Observation of patients with Sorsby's fundus dystrophy has shown that a prolonged choroidal filling phase on fluorescein angiography may indicate the presence of diffuse thickening of Bruch's membrane. We analyzed fluorescein angiography transit photographs in 100 eyes of 100 consecutive patients with age-related changes at the level of Bruch's membrane. Of these, 26 eyes had evidence of a prolonged choroidal filling phase during the initial dye transit. We suggest that this may represent a clinical correlate of diffuse thickening of Bruch's membrane, and that the two features are causally related.