In a prospective study the authors attempted to establish the incidence of cystoid macular edema (CME) in uncomplicated intracapsular cataract extraction with implantation of Choyce Mark IX lenses. Fluorescein angiography was performed after eight days, six weeks, six months, and at least one year post-operatively. Any edema found was classified as Grade I to III. Grade III CME was demonstrated in 4% of the cases studied after six weeks, though not after six months or one year, respectively. After one year, Grade II was found in 2% and Grade I in 15%, respectively. However, visual function was not impaired. At no time was there any correlation between the severity of the macular edema and visual acuity: all combinations are possible. Grade III CME evidently only impairs visual function if it persists for a prolonged period of time. Hyperfluorescence in the late phase of the angiogram permits the breakdown of the blood-aqueous barrier to be estimated semi-quantitatively.